sblock Elements - Result Question 19
####16. The reagent(s) used for softening the temporary hardness of water is(are)
(2010)
(a) $Ca _3\left(PO _4\right) _2$
(b) $Ca(OH) _2$
(c) $Na _2 CO _3$
(d) $NaOCl$
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Answer:
Correct Answer: 16. (b)
Solution:
- Among the group-1 metals, only $Li$ is able to form its nitride, $Li _3 N$. [All alkaline earth metals of group-2 form their nitride, $\left.M _3 N _2\right]$
$6 Li+N _2 \longrightarrow 2 Li _3 N$ (Ruby red solid)
(Air)
$\left[3 I _M+N _2 \longrightarrow{ }^{II} M _3 N _2\right]$
$Li^{\oplus}$ is the smallest metal ion of group-1. Smaller size of $Li^{\oplus}$ and larger size of nitride ion, $N^{3-}$, enable $Li^{\oplus}$ to polarise the spherical electron cloud of $N^{3-}$ and it gives higher stability to $Li _3 N$.
