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# What is the decreasing order of strength of the bases. $OH^{-}.NH_2^{-}.HC \equiv C^{-}$ and $CH_3 -CH_2^{-}$?

$(a) \;CH_3CH_2^{-} > NH^{-} _2 > HC \equiv C^{-} > OH^{-} \\ (b)\;HC \equiv C^{-} > CH_3CH_2^{-} > NH_2^{-} > OH^{-} \\ (c)\;OH^{-} > NH_2^{-} > HC \equiv C^{-} > CH_3CH_2^{-} \\ (d)\;NH_2 ^{-} > HC \equiv C^{-} > OH^{-} > CH_3CH_2^{-}$

The strength of their conjugate acids are in the order :
$H_2O > HC \equiv CH > NH_3 > CH_3 -CH_3$
Stronger the acid weaker is its conjugate base.
Therefore correct order of strength their conjugate bases is
$CH_3 - CH_2^{-} > NH_2^{-} > HC \equiv C^{-} > OH^{-}$
Hence a is the correct answer.