sblock Elements 1 Question 16
16. The metal that forms nitride by reacting directly with $\mathrm{N}_2$ of air, is
(2019 Main, 9 Jan II)
(a) Rb
(b) K
(c) Cs
(d) Li
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Answer:
Correct Answer: 16. (d)
Solution: Among the group- 1 metals, only Li is able to form its nitride, $\mathrm{Li}_3 \mathrm{~N}$. [All alkaline earth metals of group-2 form their nitride, $M_3 \mathrm{~N}_2$]
$\mathrm{Li}^{\oplus}$ is the smallest metal ion of group-1. Smaller size of $\mathrm{Li}^{\oplus}$ and larger size of nitride ion, $\mathrm{N}^{3-}$, enable $\mathrm{Li}^{\oplus}$ to polarise the spherical electron cloud of $\mathrm{N}^{3-}$ and it gives higher stability to $\mathrm{Li}_3 \mathrm{~N}$
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