Hydrocarbon (A) reacts with bromine by substitution to form an alkyl bromide which by Wurtz reaction is converted to gaseous hydrocarbon containing less than four carbon atoms. A is

Options

A. `CH-=CH`
B. `CH_2=CH_2`
C. `CH_3-CH_3`
D. `CH_4`

Answer

D

Explanation

(i)Since hydrocarbon (A) reacts with `Br_2` by substitution by form an alkyl bromide , therefore , hydrocarbon (A) must be either `CH_4` or `CH_3CH_3` and the alkyl bromide it forms must be either `CH_3Br` or `CH_3CH_2Br`
`CH_4+Br_2 overset"hv"to CH_3Br+HBr`
`CH_3-CH_3+Br_2 overset"hv"to CH_3CH_2Br + HBr`
(ii) Since `CH_2=CH_2` and `CH-=CH` give addition reactions on treatment with `Br_2` , therefore , hydrocarbon (A) cannot be `CH_2=CH_2` or `CH-=CH`.
(iii)Since alkyl bromide on Wurtz reaction gives a hydrocarbon containing less than four carbon atoms, therefore, alkyl halide must be `CH_3Br` and the hydrocarbon formed must be ethane.
`2CH_3Br + 2Na underset"(Wurtz reaction)"oversetDeltato underset"Ethane"(CH_3-CH_3)+ 2NaBr`