Give names of the following:
$(a)$ An alcohol containing $4$ carbon atoms.
$(b)$ An acid with $5$ carbon atoms.
$(c)$ Simplest ketone. Define functional group in a carbon compound. Mention names of any three functional groups with their formulae and example.

(N/A) Butanol.
$(b)$ Pentanoic acid.
$(c)$ Propan-$2$-one. An atom or group of atoms attached to the carbon chain by replacing one or more hydrogen atoms,which acts as a reactive site in the molecule and decides the chemical properties of the compound,is called a functional group.

Functional Group	Formula and Example
$1.$ Aldehyde	Formula: $-CHO$,Example: Ethanal $(CH_3CHO)$
$2.$ Ketone	Formula: $>C=O$,Example: Propanone $(CH_3COCH_3)$
$3.$ Carboxylic acid	Formula: $-COOH$,Example: Ethanoic acid $(CH_3COOH)$