The Correct set from the following

Question:

The Correct set from the following in which both pairs are in correct order of melting point is

  1. $\mathrm{LiF}>\mathrm{LiCl} ; \mathrm{NaCl}>\mathrm{MgO}$

  2. $\mathrm{LiF}>\mathrm{LiCl} ; \mathrm{MgO}>\mathrm{NaCl}$

  3. $\mathrm{LiCl}>\mathrm{LiF} ; \mathrm{NaCl}>\mathrm{MgO}$

  4. $\mathrm{LiCl}>\mathrm{LiF} ; \mathrm{MgO}>\mathrm{NaCl}$


Correct Option: , 2

Solution:

Generally

M.P. $\propto$ Lattice energy $=\frac{\mathrm{KQ}_{1} \mathrm{Q}_{2}}{\mathrm{r}^{+}+\mathrm{r}^{-}}$

$\propto$ (packing efficiency)

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