Question

compound A having molecular formula c3h7cl reactive to alcoholic koh.compound B having molecular formula c3h6 BE AN additional reaction with HBr GIVES C.find A,B AND C

Answer 1

In case of compound A , as it is reactive to alcoholic Cl , the Cl group must not be present at the terminal.

As there are only three carbons, the compound will be 2-chloropropane($H_3C-CHCl-CH_3$).

In case of compound  B, on seeing the formula we can say it is an alkene.
NOTE :- $C_nH_{2n}$ = $C_3H_{2*3}$

Therefore the compound B will be Propene ($H_2C=CH-CH_3$)

According to Markonikov Rule compound C will be 2-bromopropane ($H_3C-CHBr-CH_3$)

Answer 2

A is isopropyl chloride CH3CHCLCH3 it can also be npropyl alcohol CH3CH2CH2CL
then it reacts with alc. KOH and eliminates HCL to form propene CH3CH=CH2 THIS IS compound B then B reacts with HBr to give isopropyl bromide that is CH3CHBrCH3
HOPE THIS MIGHT BE UNDERSTOOD