# The order of decreasing stability of the carbanions $(CH_3)_3 C^-(I) ; (CH_3)_2CH^{-1}(II) ; CH_3CH_2^{-}(III); C_6H_5CH_2^{-} (IV)$ is

$(a)\;I > II > III > IV \\ (b)\;IV > III > II > I \\(c)\; IV > I > II > III \\ (d)\;I > II > IV > III$

Hyperconjugation decreases the heat of hydrogenation.
Lesser the heat of hydrogenation lesser is the internal energy and more is the stability of the system.
Hyperconjugation effect increases in the order.
$(CH_3)_3C^{-} < (CH_3)_2 CH^{-} < CH_3CH_2^- < C_6H_5 CH_{2}^{-}$
Therefore $IV > III > II > I$
Hence b is the correct answer.