In which of the following equilibria,$K_p$ and $K_c$ are $NOT$ equal?

When $2 \, mol$ of $PCl_5$ is heated in a closed vessel of $2 \, L$ capacity,$40\%$ of $PCl_5$ dissociates into $PCl_3$ and $Cl_2$ at equilibrium. The value of the equilibrium constant $K_c$ will be:

In the reversible reaction $A + B \rightleftharpoons C + D$,the concentration of each $C$ and $D$ at equilibrium was $0.8 \ mol/L$. If the initial concentration of $A$ and $B$ was $1 \ mol/L$ each,then the equilibrium constant $K_c$ will be:

$A$ homogeneous ideal gaseous reaction $AB_{2(g)} \rightleftharpoons A_{(g)} + 2B_{(g)}$ is carried out in a $25 \ L$ flask at $27^{\circ}C$. The initial amount of $AB_{2}$ was $1 \ mole$ and the equilibrium pressure was $1.9 \ atm$. The value of $K_{P}$ is $x \times 10^{-2}$. The value of $x$ is $...$ (Integer answer)

An amount of solid $NH_4HS$ is placed in a flask already containing ammonia gas at a certain temperature and $0.50 \ atm$ pressure. Ammonium hydrogen sulphide decomposes to yield $NH_3$ and $H_2S$ gases in the flask. When the decomposition reaction reaches equilibrium,the total pressure in the flask rises to $0.84 \ atm$. The equilibrium constant for $NH_4HS$ decomposition at this temperature is

Explain why the partial pressure $p$ of a gas is proportional to its concentration $c$.