Following are the statements with reference to ‘lipids’.

(a) Lipids having only single bonds are called unsaturated fatty acids.

(b) Lecithin is a phospholipid.

(c) Trihydroxy propane is glycerol.

(d) Palmitic acid has 20 carbon atoms including carboxyl carbon.

(e) Arachidonic acid has 16 carbon atoms.

Choose the correct answer from the options given below.

To identify the correct statements regarding lipids, let us analyze each of the given statements one by one:

Statement (a): Lipids having only single bonds are called unsaturated fatty acids.
Analysis: Fatty acids that contain only single carbon-carbon bonds in their hydrocarbon chain are called saturated fatty acids (e.g., palmitic acid). Fatty acids containing one or more double bonds are called unsaturated fatty acids. Therefore, this statement is incorrect.

Statement (b): Lecithin is a phospholipid.
Analysis: Lecithin is indeed a well-known phospholipid found in cell membranes, consisting of glycerol, two fatty acids, a phosphate group, and a choline group. Therefore, this statement is correct.

Statement (c): Trihydroxy propane is glycerol.
Analysis: Glycerol is a simple lipid molecule chemically known as propane-1,2,3-triol (or trihydroxy propane), containing three carbon atoms, each attached to a hydroxyl (–OH) group. Therefore, this statement is correct.

Statement (d): Palmitic acid has 20 carbon atoms including carboxyl carbon.
Analysis: Palmitic acid is a saturated fatty acid that has 16 carbon atoms in total, including the carboxyl carbon. Arachidonic acid has 20 carbon atoms. Therefore, this statement is incorrect.

Statement (e): Arachidonic acid has 16 carbon atoms.
Analysis: Arachidonic acid is an unsaturated fatty acid that has 20 carbon atoms, including the carboxyl carbon. Therefore, this statement is incorrect.

Based on the analysis, only statements (b) and (c) are correct.
Thus, the correct option is (b) and (c) only.