Assistant Provident Fund Commissioner and Enforcement Officer / Accounts Officer (APFC and EO/AO) 2025 recruitment test. Transcribed from the Commission's own booklet (series A, PENA-A-PTS); answer worked out by our faculty — UPSC has published no answer key for this sitting. This question is in Part B. Answer last reviewed 25 August 2026.

Which one among the following statements with regard to fatty acids is correct ?

(a)Most fatty acids have carboxyl group at one end and methyl group at the other end.
(b)Saturated fatty acids carry even number of double bonds between carbon atoms.
(c)Saturated fatty acids carry odd number of double bonds between carbon atoms.
(d)Monounsaturated fatty acids carry as many hydrogen atoms as they can.

Answer

Why

Correct — A, (a) Most fatty acids have carboxyl group at one end and methyl group at the other end. That sentence is the definition of a fatty acid put in structural terms.

A fatty acid is a carboxylic acid with a long hydrocarbon tail. At one end sits the CARBOXYL group, –COOH, which is what makes the molecule an acid and which is the end that reacts — it is esterified to glycerol to form fats and oils, and it is the end from which chemists number the carbons, C1, C2 and so on. At the far end the chain simply runs out in a METHYL group, –CH3, the terminal carbon, which biochemists call the omega carbon. The whole omega-3 and omega-6 nomenclature depends on it: the number counts carbons from the methyl end to the first double bond.

The hedge 'most' is doing honest work in the option and should not be read as weakness. The overwhelming majority of natural fatty acids are exactly of this form, but there are unusual ones — dicarboxylic acids with a carboxyl group at both ends, hydroxy and branched-chain acids — so a sentence claiming ALL would be less accurate, not more. In an option set where the other three sentences are structurally impossible, the correctly hedged sentence is the one to take.

The rest of the set turns on one word. A SATURATED fatty acid is saturated with hydrogen: every carbon–carbon bond in the chain is single, so there are no double bonds at all, and the chain holds the greatest number of hydrogen atoms it can. A MONOUNSATURATED acid has exactly one carbon–carbon double bond and therefore two hydrogens fewer, like oleic acid in olive oil; a POLYUNSATURATED acid has two or more, like linoleic and alpha-linolenic acid. Options (b), (c) and (d) each contradict one of those definitions.

Why the others are wrong

(b)Saturated fatty acids carry even number of double bonds between carbon atoms. — The option asserts that saturated fatty acids contain double bonds and that the count is even. Saturation means precisely the absence of carbon–carbon double bonds — introduce even one and the acid is by definition unsaturated. There is a real fact in the neighbourhood which is probably what the option is playing on: most naturally occurring fatty acids have an even number of CARBON ATOMS, because they are assembled two carbons at a time from acetyl units. Even carbons, not even double bonds.
(c)Saturated fatty acids carry odd number of double bonds between carbon atoms. — The same impossibility with the parity reversed, and the pair (b) and (c) is a familiar construction: two options that differ in one word, neither of which can be right, offered so that a candidate spends time choosing between them. Whatever number is put into the sentence, a saturated chain has no carbon–carbon double bonds, so no count fits.
(d)Monounsaturated fatty acids carry as many hydrogen atoms as they can. — This describes a SATURATED fatty acid, and the word 'saturated' means exactly that — filled to capacity with hydrogen. A monounsaturated acid has one double bond, and forming that bond costs the chain two hydrogen atoms, so it carries two fewer than the saturated acid of the same carbon number. Oleic acid, with eighteen carbons and one double bond, is the standard example against stearic acid, with eighteen carbons and none.

Concept

Fats and oils are triglycerides: three fatty acid chains esterified to one molecule of glycerol through their carboxyl groups. The behaviour of the fat follows from the chains. Saturated chains are straight, pack closely, and give solids at room temperature — butter, ghee, coconut and palm fat. A cis double bond puts a kink in the chain, packing is disrupted, and the melting point falls, which is why unsaturated fats are oils. Essential fatty acids — linoleic (omega-6) and alpha-linolenic (omega-3) — cannot be synthesised by the body and must come from the diet. Industrial hydrogenation adds hydrogen across double bonds to harden oils into vanaspati, and the partial hydrogenation used for that purpose is what produces trans fats, whose straightened chains behave like saturated fat.

Chemistry in the EPFO general ability paper is asked at the level of definitions and everyday applications — which acid is which, what a term means, what a substance is used for. Items of this kind are answered by taking the key word apart: 'saturated', 'mono-unsaturated' and 'carboxyl' each announce their own meaning, and three of the four options here contradict the meaning of the word they use. That makes it a reading exercise as much as a chemistry one.

This is a which-statement-is-correct item in which the statements ARE the options, so there is no numbered list to adjudicate and no codes line to eliminate against. Every option must therefore be judged on its own, and the fastest way is to test each against the meaning of its own key word: 'saturated' forbids double bonds, 'monounsaturated' fixes their number at one. Two of the four options contradict the word they contain, which is a category of error that needs no chemistry to detect. The remaining judgement — whether 'most fatty acids' is a fair statement — is settled by knowing that the hedge is there for the unusual acids that do exist.

Key facts

A fatty acid has a carboxyl group (–COOH) at one end and a terminal methyl group (–CH3) at the other.
Carbons are numbered from the carboxyl end; the omega numbering counts from the methyl end.
Saturated fatty acids have no carbon–carbon double bonds and hold the maximum possible hydrogen.
Monounsaturated fatty acids have exactly one carbon–carbon double bond; polyunsaturated have two or more.
Most naturally occurring fatty acids have an even number of carbon atoms, being built from two-carbon units.
Saturated fats are usually solid at room temperature; unsaturated fats are usually liquid, because cis double bonds kink the chain.
Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) are essential fatty acids and must come from the diet.
Fats are triglycerides — three fatty acids esterified to glycerol; partial hydrogenation of oils produces trans fats.

Study next

Saponification and the manufacture of soap from triglyceridesHydrogenation of oils, vanaspati, and why trans fats are regulatedEssential fatty acids and dietary sources of omega-3 and omega-6Lipoproteins — LDL and HDL — and how dietary fat affects themFunctional groups in organic chemistry and the naming conventions that go with them

Common traps

Reading past 'saturated' — the word by itself settles whether double bonds can be present.
Confusing the even number of carbon atoms in natural fatty acids with a count of double bonds.
Treating a hedged option like 'most' as automatically wrong; hedges are often what makes a statement accurate.
Assuming that where two options differ in one word, one of the two must be right.

Organic chemistry appears in these papers as one item on a class of compounds and one on a named substance. Both are answered from definitions rather than reactions: know what the class is, what its defining group is, and one everyday example of it. Where the options are themselves full statements, as here, there is no codes line to eliminate against, so budget a little more time and test each option against the definition of the term it uses rather than against the others.

Related PYQs

EPFO_APFC_2016_Q63

Acid rain is due to

(a) Sulphur dioxide pollution
(b) Carbon monoxide pollution
(c) Pesticide pollution
(d) Dust particles in the atmosphere

Answer(a) Sulphur dioxide pollution

A chemistry item from the same block of these papers, asked the same way — a named everyday phenomenon, acid rain, traced back to the substances that cause it.

Practice

practice — not a real PYQ
A fatty acid with exactly one carbon–carbon double bond in its chain is described as which one among the following ?
- (a)Saturated
- (b)Monounsaturated
- (c)Polyunsaturated
- (d)Trans-esterified
Answer(b) Monounsaturated
practice — not a real PYQ
Fats and oils are chemically which one among the following ?
- (a)Esters of fatty acids with glycerol
- (b)Amides of fatty acids with ammonia
- (c)Polymers of glucose
- (d)Salts of fatty acids with sodium
Answer(a) Esters of fatty acids with glycerol