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JEE Main levelSingle correct optionDifficulty 2 of 3o1020

Which of the following is a good nucleophile but a very weak base?

A $OH X^{-}$
B $I X^{-}$
C $NH X_{2} X^{-}$
D $CH X_{3} O X^{-}$

Answer: B

I X^{-}

is large and highly polarisable, hence a good nucleophile, but its conjugate acid HI (pKa about -10) is a very strong acid, so

I X^{-}

is an extremely weak base.

OH X^{-}

,

NH X_{2} X^{-}

and

CH X_{3} O X^{-}

are strong bases.

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