Saturated fatty acid is
A. Stearic acid
B. Oleic acid
C. Linoleic acid
D. Linolenic acid

Answer

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Hint: Fatty acids have been categorized into two types i.e., saturated and unsaturated based on the absence or presence of one or more double bonds in their long carbon chains. The saturated fatty acids have a general formula of

C_{n} H_{2 n} O_{2}

and the unsaturated fatty acids have a general formula of

C_{n} H_{2 n - 2 x} O_{2}

.

Complete answer:
Option (A) is correct. Stearic acid is a saturated fatty acid as its long carbon chain does not contain any double-bond and only single-bonds are present. The chemical formula of stearic acid is

C_{18} H_{36} O_{2}

.
Option (B) is incorrect. Oleic acid is a monounsaturated fatty acid as its long carbon chain contains 1 double-bond. The chemical formula of oleic acid is

C_{18} H_{34} O_{2}

.
Option (C) is incorrect. Linoleic acid is a polyunsaturated fatty acid as its long carbon chain contains 2 double-bonds. The chemical formula of linoleic acid is

C_{18} H_{32} O_{2}

.
Option (D) is incorrect. Linolenic acid is a polyunsaturated fatty acid as its long carbon chain contains 3 double-bonds. The chemical formula of linolenic acid is

C_{18} H_{30} O_{2}

.

Hence, the correct answer is option (A).

Additional information:
Difference between saturated and unsaturated fatty acids:

Saturated Fatty Acids	Unsaturated Fatty Acids
They have no carbon-carbon double bonds at all.	They have one or more carbon-carbon double bonds.
They have a higher melting point.	They have a lower melting point.
They exist in a solid-state at room temperature.	They exist in a liquid-state at room temperature.
They are mostly found in animal fats like butter, meat, milk.	They are mostly found in plant sources like mustard oil, avocado oil, sunflower oil, etc.
Hydrocarbon chains in saturated fatty acids are linear and unbranched.	Hydrocarbon chains in unsaturated fatty acids are bent and branched.

Note: Stearic acid is an 18-carbon long saturated fatty acid and its IUPAC name is octadecanoic acid. It is a waxy solid and is used as a lubricant. It is mostly used in the production of detergents, soaps, and cosmetics.