Thai O-NET Tests - วิทยาศาสตร์ - 2021 ข้อ 13

The question is in Thai language, so let me first translate it:

"Which one is a molecular formula of straight-chain saturated fatty acid found in food?"

Now, let's analyze each option:

Saturated fatty acids have the general formula CnH2nO2, where n is the number of carbon atoms.

Let's check each option:

A: C12H22O2 For a saturated fatty acid with 12 carbon atoms, the formula should be C12H24O2 (using the formula CnH2nO2). But this option has C12H22O2, which has 2 fewer hydrogen atoms than expected for a saturated fatty acid. This suggests it's an unsaturated fatty acid. So, A is incorrect.

B: C14H28O2 For a saturated fatty acid with 14 carbon atoms, the formula should be C14H28O2 (using the formula CnH2nO2). This matches option B. This corresponds to myristic acid, a common saturated fatty acid. So, B is correct.

C: C16H30O2 For a saturated fatty acid with 16 carbon atoms, the formula should be C16H32O2 (using the formula CnH2nO2). But this option has C16H30O2, which has 2 fewer hydrogen atoms than expected for a saturated fatty acid. This suggests it's an unsaturated fatty acid. So, C is incorrect.

D: C18H32O2 For a saturated fatty acid with 18 carbon atoms, the formula should be C18H36O2 (using the formula CnH2nO2). But this option has C18H32O2, which has 4 fewer hydrogen atoms than expected for a saturated fatty acid. This suggests it's an unsaturated fatty acid with 2 double bonds. So, D is incorrect.

E: C18H38O2 For a saturated fatty acid with 18 carbon atoms, the formula should be C18H36O2 (using the formula CnH2nO2). But this option has C18H38O2, which has 2 more hydrogen atoms than expected for a saturated fatty acid. This formula doesn't fit any common fatty acid structure. So, E is incorrect.

Let me double check by calculating the hydrogen atoms for each formula:

For a saturated fatty acid, the formula is CnH2nO2. The hydrogen count is 2n.

A: C12H22O2. For n=12, 2n=24, but we have 22 hydrogen atoms. This is 2 fewer than expected for a saturated fatty acid. B: C14H28O2. For n=14, 2n=28, which matches the number of hydrogen atoms in the formula. This is consistent with a saturated fatty acid. C: C16H30O2. For n=16, 2n=32, but we have 30 hydrogen atoms. This is 2 fewer than expected for a saturated fatty acid. D: C18H32O2. For n=18, 2n=36, but we have 32 hydrogen atoms. This is 4 fewer than expected for a saturated fatty acid. E: C18H38O2. For n=18, 2n=36, but we have 38 hydrogen atoms. This is 2 more than expected for a saturated fatty acid.

Wait, let me check the formula again. For saturated fatty acids, the formula is actually CnH2n+1COOH, which simplifies to CnH2n+2O2. Let me recalculate:

For a saturated fatty acid with n carbon atoms, the number of hydrogen atoms is 2n+2.

A: C12H22O2. For n=12, 2n+2=26, but we have 22 hydrogen atoms. This is 4 fewer than expected for a saturated fatty acid. B: C14H28O2. For n=14, 2n+2=30, but we have 28 hydrogen atoms. This is 2 fewer than expected for a saturated fatty acid. C: C16H30O2. For n=16, 2n+2=34, but we have 30 hydrogen atoms. This is 4 fewer than expected for a saturated fatty acid. D: C18H32O2. For n=18, 2n+2=38, but we have 32 hydrogen atoms. This is 6 fewer than expected for a saturated fatty acid. E: C18H38O2. For n=18, 2n+2=38, which matches the number of hydrogen atoms in the formula. This is consistent with a saturated fatty acid.

I think I'm mixing up the formula. Let's take a step back and be more precise. Fatty acids have the general formula R-COOH, where R is the hydrocarbon chain.

For saturated fatty acids with a straight chain of n carbon atoms:

• The hydrocarbon chain has the formula CnH2n+1-.
• COOH is the carboxylic acid group.
• Together, the formula is CnH2n+1COOH, which simplifies to CnH2n+2O2.

Wait, that's not right. The formula should be CnH2n+1COOH (with COOH being part of the n carbon atoms), which simplifies to CnH2nO2.

For example, lauric acid is a saturated fatty acid with 12 carbon atoms, and its formula is C12H24O2.

So, for a saturated fatty acid with n carbon atoms, the number of hydrogen atoms is 2n.

A: C12H22O2. For n=12, 2n=24, but we have 22 hydrogen atoms. This is 2 fewer than expected for a saturated fatty acid. B: C14H28O2. For n=14, 2n=28, which matches the number of hydrogen atoms in the formula. This is consistent with a saturated fatty acid (myristic acid). C: C16H30O2. For n=16, 2n=32, but we have 30 hydrogen atoms. This is 2 fewer than expected for a saturated fatty acid. D: C18H32O2. For n=18, 2n=36, but we have 32 hydrogen atoms. This is 4 fewer than expected for a saturated fatty acid. E: C18H38O2. For n=18, 2n=36, but we have 38 hydrogen atoms. This is 2 more than expected for a saturated fatty acid.

Based on this, option B (C14H28O2) corresponds to a straight-chain saturated fatty acid, specifically myristic acid.

Let me just double check with a few examples of known saturated fatty acids:

• Lauric acid: C12H24O2 (not among the options)
• Myristic acid: C14H28O2 (option B)
• Palmitic acid: C16H32O2 (not among the options)
• Stearic acid: C18H36O2 (not among the options)

Looking at the options, only B (C14H28O2) matches a known saturated fatty acid, which is myristic acid.

Actually, let me be even more careful and re-check the formula for saturated fatty acids.

A fatty acid has a carboxylic acid group (COOH) and a hydrocarbon chain. For a saturated fatty acid, the hydrocarbon chain has only single bonds.

The general formula for a saturated fatty acid with n carbon atoms is CnH2nO2. For example:

• Lauric acid (12 carbon atoms): C12H24O2
• Myristic acid (14 carbon atoms): C14H28O2
• Palmitic acid (16 carbon atoms): C16H32O2
• Stearic acid (18 carbon atoms): C18H36O2

Now, let's check each option: A: C12H22O2. The expected formula for a 12-carbon saturated fatty acid is C12H24O2. This has 2 fewer hydrogen atoms, indicating unsaturation. So, it's not a saturated fatty acid. B: C14H28O2. This matches the formula for myristic acid, a 14-carbon saturated fatty acid. C: C16H30O2. The expected formula for a 16-carbon saturated fatty acid is C16H32O2. This has 2 fewer hydrogen atoms, indicating unsaturation. So, it's not a saturated fatty acid. D: C18H32O2. The expected formula for an 18-carbon saturated fatty acid is C18H36O2. This has 4 fewer hydrogen atoms, indicating two points of unsaturation. So, it's not a saturated fatty acid. E: C18H38O2. The expected formula for an 18-carbon saturated fatty acid is C18H36O2. This has 2 more hydrogen atoms than expected, which doesn't fit the pattern for fatty acids. It might be a different type of compound.

Based on this analysis, the answer is B (C14H28O2).

Actually, I see the issue with my inconsistency earlier. For a fatty acid with n carbon atoms, the general formula is indeed CnH2nO2 for saturated fatty acids.

Let's check one more time: A: C12H22O2. With n=12, the expected formula is C12H24O2. This has 2 fewer hydrogen atoms, indicating it's unsaturated. B: C14H28O2. With n=14, the expected formula is C14H28O2. This matches, indicating it's a saturated fatty acid. C: C16H30O2. With n=16, the expected formula is C16H32O2. This has 2 fewer hydrogen atoms, indicating it's unsaturated. D: C18H32O2. With n=18, the expected formula is C18H36O2. This has 4 fewer hydrogen atoms, indicating it has two points of unsaturation. E: C18H38O2. With n=18, the expected formula is C18H36O2. This has 2 more hydrogen atoms, which doesn't fit the pattern for fatty acids.

Based on this, the answer is B (C14H28O2), which corresponds to myristic acid, a straight-chain saturated fatty acid.

Actually, wait. Let's be even more careful. A saturated fatty acid with n carbons has the formula CnH2nO2.

Instead of trying to reason about the number of hydrogens from the formula, let's just use this formula directly.

C12H22O2: For n=12, a saturated fatty acid would have 2n=24 hydrogens. This has 22, so it's short by 2, indicating unsaturation. C14H28O2: For n=14, a saturated fatty acid would have 2n=28 hydrogens. This matches, so it is a saturated fatty acid. C16H30O2: For n=16, a saturated fatty acid would have 2n=32 hydrogens. This has 30, so it's short by 2, indicating unsaturation. C18H32O2: For n=18, a saturated fatty acid would have 2n=36 hydrogens. This has 32, so it's short by 4, indicating two points of unsaturation. C18H38O2: For n=18, a saturated fatty acid would have 2n=36 hydrogens. This has 38, which is 2 more than expected. This is unusual and doesn't fit the pattern for fatty acids.

Based on this, the only option that corresponds to a straight-chain saturated fatty acid is B: C14H28O2.

Therefore, the correct answer key is "b".

Okay, let's tackle this question. The question is asking for the molecular formula of a straight-chain saturated fatty acid commonly found in food. The options are a through e, each with different formulas.

First, I need to recall what a saturated fatty acid is. Saturated fatty acids have no double bonds between the carbon atoms; they're "saturated" with hydrogen atoms. The general formula for a saturated fatty acid is something like CH3(CH2)nCOOH. Breaking that down, the carboxylic acid group is COOH, and the rest is a long hydrocarbon chain with only single bonds.

The molecular formula for a saturated fatty acid would then be based on this structure. Let's think about the components. The carboxylic acid part is COOH, which is C2H4O2. The hydrocarbon chain is CH3(CH2)nCH2-. Wait, actually, the entire molecule would be CH3(CH2)mCOOH. Let's count the carbons. The COOH has 2 carbons, and the rest (CH3(CH2)m) would have m + 1 carbons. So total carbons are m + 3? Wait, maybe I'm getting confused here. Let me rephrase.

A saturated fatty acid has the formula CxH2y+1COOH. Wait, no. Let's take a specific example. Palmitic acid is a common saturated fatty acid with 16 carbons. Its formula is C16H32O2. Wait, but wait, palmitic acid is CH3(CH2)14COOH. Let's count the hydrogens. Each CH2 group has 2 hydrogens, and the CH3 has 3. The COOH has two oxygen atoms. Let's see: the chain is CH3-(CH2)14-COOH. So total carbons: 1 (from CH3) + 14*1 (from each CH2) + 2 (from COOH) = 1+14+2=17? Wait, no. Wait, CH3 is one carbon, each CH2 is one carbon, so 14 CH2 groups would be 14 carbons, and COOH is two carbons (the C and O in COOH? Wait, no. The COOH is a carboxylic acid group: -COOH, which is one carbon (the C in COOH) plus the oxygen. Wait, the structure is R-COOH, where R is the alkyl chain. So if the alkyl chain is CH3(CH2)14-, then the total carbons would be 1 (CH3) + 14 (CH2) + 1 (from COOH) = 16. So palmitic acid is C16H32O2. Wait, but the formula for palmitic acid is C16H32O2. Let me check that. Each CH2 group contributes 2 hydrogens, but in a saturated chain, all single bonds. So the formula for a saturated fatty acid with n carbons would be CnH2nO2? Wait, no. Let's think again.

Take palmitic acid: 16 carbons. The formula is C16H32O2. Let's see: for a saturated hydrocarbon chain (alkane), the formula is CnH2n+2. But when you have a carboxylic acid, you replace a CH3 with a COOH group. So if the alkyl chain is (n-1) carbons, then the total would be (n-1) + 2 (from COOH) = n+1? Wait, maybe I'm overcomplicating. Let's take the example of palmitic acid again. It's CH3(CH2)14COOH. So the chain is 16 carbons in total. The formula would be C16H32O2. Let's count the hydrogens. Each CH3 has 3 H, each CH2 has 2 H, and the COOH has a COOH group. Wait, the COOH group is -COOH, which has two oxygen atoms. The carbon in COOH is connected to two oxygen atoms (one double-bonded O and one -OH group). So the structure is:

CH3-(CH2)14-COOH

Each CH2 group contributes 2 H, and there are 14 of them. The CH3 has 3 H. The COOH group: the carbon in COOH is bonded to two oxygen atoms and the adjacent CH2. So the COOH carbon has one H (since it's connected to three other groups: O, O-, and the chain). Wait, maybe I'm getting stuck here. Alternatively, perhaps the general formula for a saturated fatty acid is CnH2nO2. Wait, no. Let's think of the degree of saturation. A saturated fatty acid has no double bonds, so the formula would follow the alkane pattern but with the carboxylic acid group.

For an alkane, the formula is CnH2n+2. If we have a carboxylic acid, which replaces a CH3 group with COOH, then the formula would be CnH2nO2. Wait, let's see. For example, if we have a 16-carbon saturated fatty acid (palmitic acid), the formula is C16H32O2. Let's check: 16 carbons, 32 hydrogens, 2 oxygens. How does that fit? If n=16, then 2n would be 32, so H=32. So the formula would be CnH2nO2. So for a saturated fatty acid, the formula is CnH2nO2. Therefore, the general formula is CxH2xO2. So looking at the options:

a: C12H22O2 → 2x=22 → x=11. So n=11. But 11+1 (since the formula is CnH2nO2, n would be the number of carbons. Wait, maybe I'm mixing up. If the formula is CnH2nO2, then for palmitic acid (C16H32O2), n=16, 2n=32. So yes, that works. So the formula for a saturated fatty acid is CnH2nO2. Therefore, looking at the options:

a: C12H22O2 → 2n=22 → n=11. So 11 carbons. But 11 is possible, but common ones are 16, 18, etc.

b: C14H28O2 → 2n=28 → n=14. So 14 carbons. Myristic acid is C14H28O2.

c: C16H30O2 → 2n=30 → n=15. But that would imply 15 carbons, but 2n=30 → n=15. Wait, but 15 carbons would be pentadecanoic acid, which is C15H30O2. Wait, but option c is C16H30O2. That would be 16 carbons, but 2n=30 → n=15. That doesn't fit. So this would be an odd number of carbons? Or maybe I'm miscalculating.

Wait, maybe the formula isn't exactly CnH2nO2. Let's think again. The general formula for a saturated fatty acid (straight chain) is CH3(CH2)mCOOH. Let's count the hydrogens. The CH3 has 3 H, each CH2 in the (CH2)m has 2 H each (total 2m), and the COOH has a structure where the carbon is bonded to two oxygens and one CH2. The COOH group's carbon has two oxygen atoms (one double bond, one -OH). So the COOH group contributes one H (from the -OH) and the carbon in COOH has two bonds (double bond to O and single to OH). Wait, maybe this is getting too detailed. Alternatively, let's count the hydrogens in the entire molecule.

Take palmitic acid: CH3(CH2)14COOH. Let's break it down:

• CH3: 3 H
• Each of the 14 CH2 groups: 2 H each → 14*2=28 H
• The COOH group: The COOH has a structure of -CH2-COOH? Wait, no. The chain is CH3-(CH2)14-COOH. So the last CH2 before COOH is part of the (CH2)14. Then the COOH is -COOH. So the COOH group's carbon is connected to the (CH2)14 chain. So the COOH group's structure is:

R-COOH, where R is CH3(CH2)14-.

So the COOH group has two oxygen atoms and one H (from the -OH). But how many hydrogens are on the COOH carbon? The COOH carbon is connected to the R group, a double-bonded O, an -OH group, and another O (from the carbonyl). Wait, no. The COOH group is:

O || C-OH

So the carbon in COOH is double-bonded to one O, single-bonded to an -OH group, and single-bonded to the R group (the alkyl chain). So that carbon has no hydrogens attached. Therefore, the COOH group contributes no hydrogens except the -OH's H, which is part of the O in the formula.

Wait, but in the molecular formula, H is counted regardless of where it is. So the -OH's H is part of the H count. So let's count all H in the molecule.

For palmitic acid: CH3-(CH2)14-COOH.

Breaking it down:

• CH3: 3 H
• Each CH2 in the 14 CH2 groups: each has 2 H → 14*2=28 H
• The COOH group: The COOH has a structure where the carbonyl group (C=O) and the hydroxyl (-OH). The carbon adjacent to the COOH (the one in the chain) is a CH2 connected to the COOH. Wait, maybe I need to draw it out mentally.

The full structure is:

CH3-(CH2)14-COOH

So the chain is 16 carbons in total: 1 (CH3) + 14 (CH2) + 1 (COOH) = 16 carbons.

Now, counting hydrogens:

• CH3: 3 H
• Each of the 14 CH2 groups: each has 2 H → 14*2=28 H
• The COOH group: The carbon in COOH is connected to the chain (CH2), a double bond O, an -OH group, and another O (from the carbonyl). So that carbon has no H. The -OH group has one H. Additionally, the CH2 that connects to the COOH (the last CH2 in the chain) has 2 H. Wait, no. The chain is CH3-(CH2)14-COOH. The (CH2)14 means there are 14 CH2 groups between the CH3 and the COOH. So the COOH is attached to the last CH2. So the last CH2 is part of the 14, so each of those 14 CH2 groups has 2 H. Then the COOH is attached to that last CH2. So the COOH's carbon is connected to that CH2, which has 2 H. Wait, no. The structure is:

CH3-CH2-CH2-...-CH2-COOH (with 14 CH2 groups after the CH3)

Wait, no. The CH3 is the first carbon, then 14 CH2 groups, then the COOH. So the total carbons are 1 (CH3) + 14 (CH2) + 1 (COOH) = 16. Each CH2 group has 2 H. The COOH group's carbon has no H, but the adjacent CH2 (the 14th one) has 2 H. The COOH group has an -OH with one H. So total H:

CH3: 3

14 CH2 groups: 14*2=28

The last CH2 (the one connected to COOH): 2 H (but this is already counted in the 14 CH2 groups)

COOH: the -OH contributes 1 H.

So total H = 3 + 28 + 1 = 32. Which matches palmitic acid's formula C16H32O2.

So the general formula for a saturated fatty acid with n carbons is CnH2nO2. Because for n=16, 2n=32. So yes, the formula is CnH2nO2.

Now, looking at the options:

a: C12H22O2 → 2n=22 → n=11. So 11 carbons. Possible, but common ones are 12, 14, 16, 18.

b: C14H28O2 → 2n=28 → n=14. So 14 carbons. Myristic acid is C14H28O2.

c: C16H30O2 → 2n=30 → n=15. So 15 carbons. But 15 is an odd number. Saturated fatty acids usually have even numbers of carbons because they're synthesized from two-carbon units. So this might be a distractor.

d: C18H32O2 → 2n=32 → n=16. Wait, 2n=32 → n=16, but the formula here is C18H32O2. That would imply n=16, but the carbon count is 18. That doesn't fit. So this would be a discrepancy. Wait, maybe this is an unsaturated fatty acid. Because if it's C18H32O2, then 2n=32 → n=16, but the carbons are 18. So that would mean two double bonds? Because for each double bond, you lose two hydrogens. For example, a monounsaturated fatty acid with 18 carbons would have one double bond, so formula C18H34O2. If this is C18H32O2, that's two double bonds, making it polyunsaturated. But the question is about saturated, so this option is likely unsaturated.

e: C18H38O2 → 2n=38 → n=19. But 19 is odd. Again, unlikely for a natural fatty acid. Also, 18 carbons but 38 hydrogens. For a saturated fatty acid with 18 carbons, the formula should be C18H36O2. Because 2n=36 → n=18. But option e is C18H38O2, which would imply 2n=38 → n=19, but the carbons are 18. So this doesn't fit. This might be a trick option.

So the correct answer should be either a, b, c, d, or e based on the formula. But common saturated fatty acids are:

• Lauric acid (12 carbons): C12H24O2. But option a is C12H22O2, which would be 2n=22 → n=11. So that's not matching.

Wait, lauric acid is C12H24O2. So if the formula is CnH2nO2, then for n=12, it's C12H24O2. But option a is C12H22O2, which is two hydrogens short. That suggests a double bond, but the question is about saturated. So option a is not correct.

Myristic acid (14 carbons): C14H28O2. That's option b. Which fits CnH2nO2 with n=14. So that's correct.

Palmitic acid (16 carbons): C16H32O2. Which would be option not listed here. Looking at the options, option c is C16H30O2. That's two hydrogens less than expected, implying a double bond. So option c is unsaturated.

Stearic acid (18 carbons): C18H36O2. But option d is C18H32O2 (which is four hydrogens less, implying two double bonds), and option e is C18H38O2 (which has two extra hydrogens, which doesn't make sense).

So the only option that fits the saturated formula is option b: C14H28O2 (myristic acid) and option e is incorrect. Wait, but wait, option e is C18H38O2. Let's check that. If n=19, then 2n=38, but the carbons are 18. That's impossible. So option e is invalid.

So the correct answer should be option b: C14H28O2. But wait, the question says "found in food". Common saturated fatty acids in food include lauric (12), myristic (14), palmitic (16), and stearic (18). So option b is myristic acid, which is found in food. So the answer is b.

First, the user has provided a multiple-choice question in JSON format, similar to the previous one. It's in Thai, but I need to understand it to provide the correct answer.

The question is: "ข้อใดเป็นสูตรโมเลกุลของกรดไขมันอิ่มตัวแบบโซ่ตรงที่พบได้ในอาหาร"

Translating that to English: "Which of the following is the molecular formula of a saturated straight-chain fatty acid found in food?"

Options:

a: C12H22O2

b: C14H28O2

c: C16H30O2

d: C18H32O2

e: C18H38O2

I need to recall what a saturated straight-chain fatty acid is. Saturated fatty acids have no double bonds between carbon atoms, so they follow the general formula for alkanes but with a carboxylic acid group.

The general formula for a saturated fatty acid is CnH2nO2, where n is the number of carbon atoms in the chain, including the carboxyl carbon.

For a straight-chain saturated fatty acid, the formula is CnH2nO2 for a monocarboxylic acid.

More precisely, for a saturated fatty acid with n carbon atoms total (including the carboxyl carbon), it's CnH2nO2. But let's verify with common examples.

For example:

• Lauric acid: C12H24O2 (n=12, so H=2*12=24? Wait, no.

The standard general formula for a saturated fatty acid is CnH2nO2, but that's not accurate. Let's think:

A straight-chain saturated fatty acid has the formula CH3(CH2)nCOOH.

For n carbon atoms in total, it's C_n H_{2n} O2, but wait:

For acetic acid: C2H4O2 (n=2, H=4=2*2)

For propionic acid: C3H6O2 (n=3, H=6=2*3)

For butyric acid: C4H8O2 (n=4, H=8=2*4)

So yes, general formula: CnH2nO2 for a straight-chain saturated fatty acid with n carbon atoms.

In the options:

a: C12H22O2 → For n=12, it should be C12H24O2 (2*12=24), but it's H22, which is less.

b: C14H28O2 → For n=14, 2*14=28, so C14H28O2 matches.

c: C16H30O2 → For n=16, 2*16=32, so it should be C16H32O2, but it's H30.

d: C18H32O2 → For n=18, 2*18=36, so C18H36O2, but it's H32.

e: C18H38O2 → For n=18, 218=36, so C18H36O2, but it's H38? Wait, no: 218=36, so H38 is more.

Let's double-check.

For CnH2nO2, for n=18, it should be C18H36O2.

But option e is C18H38O2, which has 38 hydrogens, more than 36.

That doesn't make sense for a saturated fatty acid.

Perhaps I have the formula wrong.

Standard saturated fatty acids:

• Palmitic acid: C16H32O2

• Stearic acid: C18H36O2

Yes!

So, for C12: Lauric acid is C12H24O2

But option a is C12H22O2, which has only 22 H, suggesting one double bond or something.

The general formula for saturated is CnH2nO2, but for n total carbons, yes.

Let's confirm the options:

a: C12H22O2 - This looks like it has one double bond, because for saturated C12, it should be C12H24O2.

The difference: saturated has 2n H, unsaturated has less.

For example, oleic acid is C18H34O2, which is unsaturated (one double bond, so 2 less H than C18H36O2).

So, let's check:

For a: C12H22O2 vs saturated C12H24O2, so it has 2 less H, meaning one double bond.

b: C14H28O2 vs saturated C14H28O2? For n=14, saturated is C14H28O2 exactly.

Yes!

c: C16H30O2 vs saturated C16H32O2, so 2 less H, one double bond.

d: C18H32O2 vs saturated C18H36O2, so 4 less H, two double bonds.

e: C18H38O2 vs saturated C18H36O2, wait, H38 is more than H36? That doesn't make sense for a fatty acid.

C18H38O2 isn't a standard fatty acid formula. Fatty acids are CnH2nO2 for saturated, so C18H36O2.

Perhaps it's a typo or something, but let's see.

For e: C18H38O2, that would be like C18H38 for the hydrocarbon, which is alkane, but with O2, it's not standard.

I think e is incorrect.

The question is for saturated straight-chain fatty acid found in food.

From the options, only b: C14H28O2 matches the formula for a saturated fatty acid, which is myristic acid, C14H28O2, and it is found in food, like in coconut oil or milk fat.

a: C12H22O2 is like lauric acid but unsaturated, which is not saturated.

c: C16H30O2 is palmitoleic acid or something, unsaturated.

d: C18H32O2 might be linoleic acid, which has two double bonds.

e: C18H38O2 doesn't match any standard fatty acid; it's over-hydrogenated.

So, the correct one is b: C14H28O2.

Is C14H28O2 indeed saturated? Yes, myristic acid is saturated.

To confirm:

• Saturated: no double bonds, formula CnH2nO2

For b: C14H28O2, n=14, 2n=28, yes.

Others don't match.

So, the correct answer is b.

Now, as per the instructions, I need to provide a brief explanation, then respond in JSON with the "correct_answer_key".

First, brief explanation: "A saturated straight-chain fatty acid has the general formula CnH2nO2. Among the options, only C14H28O2 fits this formula, corresponding to myristic acid, which is found in foods like coconut oil."

Then, respond in JSON: {"correct_answer_key":"b"}

Finally, output it as in the example.

Okay, let's tackle this question. The user is asking which molecular formula corresponds to a straight-chain saturated fatty acid found in food. The options are a through e with different carbon and hydrogen counts.

First, I remember that fatty acids are named based on their carbon atoms. Saturated means no double bonds, so the maximum number of hydrogens. The general formula for a saturated fatty acid is CnH2n+1COOH. Wait, actually, the whole molecule would be CnH2n+1COOH, but when you combine that, the total formula would be C(n+2)H2n+2O2. Wait, let me think again. The fatty acid is a carboxylic acid with a straight chain. The general formula for a saturated fatty acid with n carbons in the chain would be CnH2n+1COOH. So combining the chain and the COOH group, the total carbons are n + 2 (since COOH has one C). The hydrogens: the chain has 2n+1 H, and the COOH group adds 2 more H (since -COOH is -COOH, which has 2 H in the carbonyl and the OH). Wait, maybe I should break it down differently.

Alternatively, the molecular formula for a saturated fatty acid is usually written as CnH2n+1COOH, so combining, the total formula would be C(n+2)H(2n+2)O2. Because the chain is n carbons, plus the 2 from the COOH (the carbonyl and the oxygen). Wait, no, the COOH is part of the chain's end. Let me think of an example. For example, palmitic acid is a common saturated fatty acid with 16 carbons. Its formula is C16H32O2. Let's see: n is 16, so plugging into C(n)H2n+2O2? Wait, palmitic acid is C16H32O2. So 2n+2 would be 216 +2 = 34? Wait that doesn't add up. Wait, maybe the formula is CnH2n+2O2. For palmitic acid (16 carbons), that would be 16 carbons, 216 +2 = 34 hydrogens. But palmitic acid is actually C16H32O2. Hmm, so maybe I made a mistake here. Let me check again.

The general formula for a saturated fatty acid is CnH2n+1COOH. The chain part is -CH2-, so for a straight-chain with n carbons in the fatty acid (excluding the COOH?), wait no. Let me clarify. The fatty acid is a straight chain of n carbons, with the COOH group at one end. So the total number of carbons is n + 2? Wait no, the COOH is part of the chain. Let's take a simple example: acetic acid is CH3COOH, which is a 2-carbon fatty acid. Its formula is C2H4O2. So for n=2, the formula is C2H4O2. Following the formula CnH2nO2. Wait, that works here. For palmitic acid, which is 16 carbons, that would be C16H32O2 (since 216=32). That matches. So the general formula is CnH2nO2. Wait, but wait, the formula for a saturated fatty acid with n carbons is CnH2n+1COOH. Let me count the hydrogens again. The COOH group is -COOH, which has 2 H (the -OH and the H on the carbonyl? No, the carbonyl is O double bond O, so the actual structure is -COOH: the carbon has two oxygens, one double bond, so the structure is R-COOH. The carbon in the COOH group has two oxygens: one double bond to O, and a single bond to -OH. So the carbon in the COOH group has two bonds: one to the previous carbon (the chain), one double bond to O, and two single bonds: one to O (as in -O-) and one to the -OH. Wait, maybe I'm overcomplicating. Let's just count the hydrogens for palmitic acid. Palmitic acid is CH3(CH2)14COOH. Wait, no, palmitic is 16 carbons total. The chain is 16 carbons, so the structure is CH3-(CH2)14-COOH. Wait, that would be 16 carbons: the CH3 is 1, then 14 CH2, and the COOH is the 16th? Wait, no. Let me count again. The COOH is part of the chain. So the total chain length is n, so for palmitic acid (16 carbons), the structure is CH3-(CH2)14-COOH. Wait, that would be 1 (CH3) +14 (CH2) +1 (the COOH's carbon) = 16. So the COOH group's carbon is the 16th. The hydrogens: each CH2 has 2 H, except the first and last. The first carbon (CH3) has 3 H. Then each CH2 in the chain (there are 14 CH2 groups between the first and the COOH) each have 2 H. The last carbon (the one in COOH) is connected to the COOH group. The COOH group is -COOH, so the carbon there has two oxygens and one -OH. So the carbon in the COOH has two oxygens (one double bond, one single bond to O), and the -OH. So the number of H on that carbon is 2 (since the carbon has four bonds: one to the previous CH2, one double bond to O, one single bond to O (as in -O-), and one -OH. Wait, actually, the structure is R-CH2-COOH. The last carbon (the one before COOH) is CH2, and the COOH is on the next carbon. Wait, maybe I'm getting confused here. Let me just look up the formula for palmitic acid. Palmitic acid is C16H32O2. So 16 carbons, 32 hydrogens. The formula CnH2nO2. So for n=16, 216=32. So the general formula is CnH2nO2. So the question is asking for a straight-chain saturated fatty acid found in food. The options are:

a: C12H22O2 → 12*2=24, but H is 22. That's 2 less. So that would be unsaturated? Because each double bond reduces 2 H. So if it's supposed to be saturated, the H should be 2n. So 12 carbons would need 24 H. Option a has 22, so that's unsaturated. So a is out.

b: C14H28O2 → 14*2=28. So that's correct for a saturated 14-carbon. So that's possible.

c: C16H30O2 → 16*2=32. So this has 30 H, which is 2 less. So that would be unsaturated (one double bond). So not saturated.

d: C18H32O2 → 18*2=36. So 32 is 4 less. So that's two double bonds. So unsaturated.

e: C18H38O2 → Wait, 18*2=36, but H is 38? That's more than 2n. That can't be. Wait, maybe I miscalculated. Wait, 18 carbons, H is 38. 2n would be 36, so 38 is 2 more. That's impossible because saturated should be 2n. So maybe a typo? Or perhaps I'm misunderstanding. Wait, maybe the formula is written differently. Let me check each option again.

Wait, the options given are:

a: C12H22O2 → 12*2=24 H needed for saturated. 22 is 2 less → unsaturated.

b: C14H28O2 → 14*2=28 → correct for saturated.

c: C16H30O2 → 16*2=32 → 30 is 2 less → unsaturated.

d: C18H32O2 → 18*2=36 → 32 is 4 less → two double bonds.

e: C18H38O2 → 182=36 → 38 is 2 more. That's impossible because even in cyclopropane-like structures, but fatty acids are straight chains. So maybe that's a mistake, but perhaps I made an error here. Wait, maybe the formula is written as CnH2n+2O2? Wait, no, the standard formula for a saturated fatty acid is CnH2n+2O2? Wait, let me think again. Wait, maybe I got the formula wrong. Let me think of a simple one. Acetic acid is CH3COOH, which is C2H4O2. So 2 carbons, 4 H. So 2n would be 4, so that's correct. For palmitic acid (16 carbons), C16H32O2. 162=32. So yes, the formula is CnH2nO2. So any H count higher than 2n is impossible. So option e has 38 H for 18 carbons, which would be 218=36, so 38 is 2 more. That's impossible. So e is invalid. So the only one that fits the saturated formula is option b (C14H28O2) and maybe another. Wait, looking back, option d is C18H32O2. 182=36, so 32 is 4 less. So that's two double bonds. So not saturated. So the correct answer must be option b. But wait, the question says "found in food". Common saturated fatty acids include palmitic acid (C16), stearic acid (C18), lauric acid (C12), myristic acid (C14). Wait, palmitic is C16H32O2, which would be option d? Wait no, option d is C18H32O2. Wait, palmitic is 16 carbons, so C16H32O2. Looking at the options, option c is C16H30O2, which is unsaturated. So the correct saturated would be C16H32O2, but that's not listed. Wait, the options given are:

a: C12H22O2 → 12 carbons, which would be lauric acid. But H is 22, which is 2 less than 24 (so unsaturated). So not correct.

b: C14H28O2 → 14 carbons, which is myristic acid. Saturated would have 28 H. So that's correct.

c: C16H30O2 → palmitic acid would need 32 H, so this is unsaturated.

d: C18H32O2 → stearic acid is C18H36O2 (since 18*2=36). So this has 32 H, which is 4 less → two double bonds. So unsaturated.

e: C18H38O2 → impossible.

Wait, so the only one that matches a saturated formula is option b (C14H28O2), which is myristic acid. But wait, maybe I made a mistake here. Let me confirm the actual formulas:

• Lauric acid (C12): C12H24O2. So option a has 22 H → unsaturated.

• Myristic acid (C14): C14H28O2 → that's option b, which is correct for saturated.

• Palmitic acid (C16): C16H32O2 → not listed as an option. The closest is option c with 30 H (unsaturated).

• Stearic acid (C18): C18H36O2 → not listed. Option d has 32 H (so two double bonds).

So the correct answer here is option b. But wait, the question is in Thai, and the options are given as:

The question is asking for the molecular formula of a straight-chain saturated fatty acid found in food. The options are:

a: C12H22O2 → unsaturated (since 12*2=24, so 22 is -2 H → one double bond)

b: C14H28O2 → correct for saturated (14*2=28)

c: C16H30O2 → unsaturated (needs 32 H)

d: C18H32O2 → unsaturated (needs 36 H)

e: C18H38O2 → impossible (too many H)

Therefore, the correct answer is option b. But wait, I thought palmitic acid (C16) is common in foods like animal fats. But palmitic acid's formula isn't listed here. The options given don't have C16H32O2. The closest is option c which is unsaturated. So the only correct saturated formula here is option b (C14H28O2), which is myristic acid. Myristic acid is found in some foods like coconut oil and dairy products. So the answer should be option b.

Alright! Let's tackle this chemistry question. The user is asking about the molecular formula of a saturated fatty acid found in food. Saturated fatty acids have single bonds between carbon atoms, which means their general formula is CₙH₂ₙO₂.

Looking at the options:

• Option A: C12H22O2. Plugging into the formula, n would be 12. But 2n would be 24, not 22. So this doesn't fit.
• Option B: C14H28O2. Here, n=14. 2n=28, which matches the hydrogen count. This works.
• Option C: C16H30O2. For n=16, 2n=32, but there are only 30 hydrogens. Doesn't fit.
• Option D: C18H32O2. n=18, 2n=36, but there are 32 hydrogens. Doesn't fit.
• Option E: C18H38O2. n=18, 2n=36, but there are 38 hydrogens. Doesn't fit.

So, the correct answer should be option B, C14H28O2.