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# The arrangement of $(CH_3)_3C-,(cH_3)_2CH-,CH_3CH_2-$ when attached to benzene or an unsaturated group, in increasing order of inductive effect is

$(a)\;(CH_3)_3C - < (CH_3)_2 CH - < CH_3CH_2 - \\(b)\;CH_3CH_2 - < (CH_3)_2 CH - < (CH_3)_3 C- \\(c)\;(CH_3)_2 CH - < (CH_3)_3 C - < CH_3CH_2 - \\(d)\;(CH_3)_3 C - < (CH_3)CH_2 - < (CH_3)_2 CH-$

Toolbox:
• In general, greater the number of alkyl groups attached to a positively charged carbon atom, the greater is the hyperconjugation interaction and stabilisation of the cation.
Hyperconjugation effect increases in the order :
$(CH_3)_3C - < (CH_3)_2 CH - < CH_3CH_2 -$
The σ electrons of C—H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p orbital.
Hence (A) is the correct answer.
edited Mar 25, 2014