KEAM 2011 Physics and Chemistry Paper

The percentage composition of compounds X and Y
 C    :  H

12

13

×100% : 

1

3

×100%
i.e., the ratio of masses of C and H in the organic compounds
 C  :  H
 

12

13

  :  

1

3

or 12:1
Thus, the empirical formula of the compounds X and Y is CH and X decolourise bromine water while Y does not. Thus, X and Y must be acetylene (CH≡CH) and benzene (C6H6) respectively.