The relationship between ${\text{K}}_{\text{p}}$ and ${\text{K}}_{\text{c}}$ is given as $\Rightarrow {\text{K}}_{\text{p}}\text{=}{\text{K}}_{\text{c}}{\text{(RT)}}^{\text{Δn}}\text{.}$

When, $\Delta \text{n}\text{=}$ moles of gaseous species and $\Delta \text{n}\text{=}$ (moles of product) - (moles of reactant) For the reaction, ${\text{NH}}_{\text{4}}\text{Cl(s)}\to {\text{NH}}_{\text{3}}\text{(g)}\text{+}\text{HCl(g)}$

we have 2 moles of gaseous species in the product side and none in the reactant side.

$\therefore \text{Δn}\text{=}\text{2}-\text{0}\text{=}\text{2}$

Hence, 2 is the correct option