Question

The order of increasing acidic strength of $C{H}_4,N{H}_3,H_{2}O,HF$ is :

• A. $C{H}_4<N{H}_3<H_{2}O<HF$
• B. $HF<N{H}_3<H_{2}O<C{H}_4$
• C. $HF<C{H}_4<H_{2}O<N{H}_3$
• D. $N{H}_3<H_{2}O<C{H}_4<HF$

Answer 1

The correct option is A $C{H}_4<N{H}_3<H_{2}O<HF$

To predict their lewis acidities we shall evaluate the relative basicities of their conjugate bases, viz.$C{H}_3^{-},N{H}_2^{-},O{H}^{-},F^{-}$
although size of central atom decreases from $C$ to $F$, volume available to electron on the central atom decreases in he order: $C,N,O,F$
Thus the increasing basic character of these conjugate bases are $C{H}_3^{-}>N{H}_2^{-}>O{H}^{-}>F^{-}$
hence, order of increasing acidic strength is $C{H}_4<N{H}_3<H_{2}O<HF$