Q97 / 200 · NEET 2010 (Screening) · Chemistry

In which of the following pairs of molecules/ions, the central atoms have $\mathrm{sp}^2$ hybridisation?

  • A
    $\mathrm{NO}_2^{-}$and $\mathrm{NH}_3$
  • Correct answer
    B
    $\mathrm{BF}_3$ and $\mathrm{NO}_2^{-}$
  • C
    $\mathrm{NH}_2^{-}$and $\mathrm{H}_2 \mathrm{O}$
  • D
    $\mathrm{BF}_3$ and $\mathrm{NH}_2^{-}$

Solution

Key Idea For $\mathrm{sp}^2$ hybridisation, there must be $3 \sigma$-bonds or $2 \sigma$-bonds along with a lone pair of electrons. (i) $\mathrm{NO}_2^{-} \Rightarrow 2 \sigma+1 \mathrm{lp}=3$, ie, $\mathrm{sp}^2$ hybridisation (ii) $\mathrm{NH}_3 \Rightarrow 3 \sigma+1 \mathrm{lp}=4$, ie, $\mathrm{sp}^3$ hybridisation (iii) $\mathrm{BF}_3 \Rightarrow 3 \sigma+0 \mathrm{lp}=3$, ie, $\mathrm{sp}^2$ hybridisation (iv) $\mathrm{NH}_2^{-} \Rightarrow 2 \sigma+2 \mathrm{lp}=4$, ie, $\mathrm{sp}^3$ hybridisation (v) $\mathrm{H}_2 \mathrm{O} \Rightarrow 2 \sigma+2 \mathrm{lp}=4$, ie, $\mathrm{sp}^3$ hybridisation Thus, among the given pairs, only $\mathrm{BF}_3$ and $\mathrm{NO}_2^{-}$ have $\mathrm{sp}^2$ hybridisation.

Hence, the correct answer is option: 'B'.

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