Give the equilibrium constant expression for the following reactions:
$(a)$ $Ni_{(s)} + 4CO_{(g)} \rightleftharpoons Ni(CO)_{4_{(g)}}$
$(b)$ $Ag_{2}O_{(s)} + 2HNO_{3_{(aq)}} \rightleftharpoons 2AgNO_{3_{(aq)}} + H_{2}O_{(l)}$

(N/A) For equilibrium constant expressions,the concentration of pure solids and pure liquids is taken as unity $(1)$ and is omitted from the expression.
$(a)$ For the reaction $Ni_{(s)} + 4CO_{(g)} \rightleftharpoons Ni(CO)_{4_{(g)}}$:
$K_{c} = \frac{[Ni(CO)_{4}]}{[CO]^{4}}$ and $K_{p} = \frac{p_{Ni(CO)_{4}}}{(p_{CO})^{4}}$
$(b)$ For the reaction $Ag_{2}O_{(s)} + 2HNO_{3_{(aq)}} \rightleftharpoons 2AgNO_{3_{(aq)}} + H_{2}O_{(l)}$:
Since $Ag_{2}O$ is a solid and $H_{2}O$ is a pure liquid,their concentrations are constant.
$K_{c} = \frac{[AgNO_{3}]^{2}}{[HNO_{3}]^{2}}$