(a) To prevent the misuse of alcohol supplied for industrial purposes, it is made unfit for drinking. This can be done by mixing it with poisonous substances such as copper sulphate, methanol, pyridine, etc. The alcohol thus obtained is called denatured alcohol.
(b) Decarboxylation means removal of carboxyl group. The reaction is classified as a decarboxylation reaction because in this process, gets removed from the acid due to which the whole carboxyl group gets removed. Thus, it gets converted to hydrocarbon methane.
(c) The peculiar smell observed near the preserved specimens in biology laboratory is due to formalin. Formalin is the aqueous solution of formaldehyde and has pungent smell.