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.

The correct answer is (b) and (c) only.

Let us analyze each statement step-by-step to understand why this option is correct:

Statement (a): "Lipids having only single bonds are called unsaturated fatty acids."
This statement is incorrect. Fatty acids with only single bonds between carbon atoms in their hydrocarbon chain are called saturated fatty acids. Fatty acids containing one or more double bonds are called unsaturated fatty acids.

Statement (b): "Lecithin is a phospholipid."
This statement is correct. Lecithin is a phosphorus-containing lipid (phospholipid) found commonly in cell membranes.

Statement (c): "Trihydroxy propane is glycerol."
This statement is correct. Glycerol is a simple lipid structure chemically known as trihydroxypropane. Its chemical formula is:
${\mathrm{CH}}_2\mathrm{OH}-\mathrm{CHOH}-{\mathrm{CH}}_2\mathrm{OH}$
It consists of a propane backbone with a hydroxyl (-OH) group attached to each carbon atom.

Statement (d): "Palmitic acid has 20 carbon atoms including carboxyl carbon."
This statement is incorrect. Palmitic acid is a saturated fatty acid that has 16 carbon atoms including the carboxyl carbon.

Statement (e): "Arachidonic acid has 16 carbon atoms."
This statement is incorrect. Arachidonic acid is an unsaturated fatty acid that has 20 carbon atoms including the carboxyl carbon.

Therefore, only statements (b) and (c) are correct, which corresponds to the option (b) and (c) only.