Concentration of a gas is expressed in which of the following terms in the calculation of the equilibrium constant?

$4.5$ moles each of hydrogen and iodine are heated in a sealed $10 \ L$ vessel. At equilibrium,$3$ moles of $HI$ are found. The equilibrium constant for ${H_2}_{(g)} + {I_2}_{(g)} \rightleftharpoons 2HI_{(g)}$ is

At $298 \ K$,for the reaction $Ag^{+} + 2NH_3 \rightleftharpoons Ag(NH_3)_2^{+}$,the concentrations of $Ag^{+}$,$Ag(NH_3)_2^{+}$,and $NH_3$ are $10^{-1} \ M$,$10^{-1} \ M$,and $10^3 \ M$ respectively. The value of $K_c$ at $298 \ K$ for this equilibrium is ...... .

Given that the equilibrium constant for the reaction,$2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)}$ has a value of $278$ at a particular temperature. What is the value of the equilibrium constant for the following reaction at the same temperature? $SO_{3(g)} \rightleftharpoons SO_{2(g)} + \frac{1}{2} O_{2(g)}$

An equilibrium mixture of the reaction $2H_2S_{(g)} \rightleftharpoons 2H_{2(g)} + S_{2(g)}$ had $0.5 mol$ $H_2S$,$0.10 mol$ $H_2$,and $0.4 mol$ $S_2$ in a $1 L$ vessel. The value of the equilibrium constant $(K_c)$ in $mol L^{-1}$ is:

For a chemical reaction $A \rightleftharpoons B, K_1 = 2.0$ and $B \rightleftharpoons C, K_2 = 0.01$. The equilibrium constant for the reaction $2C \rightleftharpoons 2A$ is $:-$