Before any reaction takes place,the value of the reaction quotient $(Q_c)$ is ......

Given the reaction between $2$ gases represented by $A_2$ and $B_2$ to give the compound $AB_{(g)}$:
$A_{2(g)} + B_{2(g)} \rightleftharpoons 2AB_{(g)}$
At equilibrium,the concentrations are $[A_2] = 3.0 \times 10^{-3} \, M$,$[B_2] = 4.2 \times 10^{-3} \, M$,and $[AB] = 2.8 \times 10^{-3} \, M$.
If the reaction takes place in a sealed vessel at $527^{\circ}C$,then the value of $K_c$ will be:

For the reaction $A + 2B \rightleftharpoons C$,the expression for the equilibrium constant is.........

$A$ sample of pure $PCl_{5}$ was introduced into an evacuated vessel at $473 \, K$. After equilibrium was attained,the concentration of $PCl_{5}$ was found to be $0.5 \times 10^{-1} \, mol \, L^{-1}$. If the value of $K_{c}$ is $8.3 \times 10^{-3}$,what are the concentrations of $PCl_{3}$ and $Cl_{2}$ at equilibrium?
$PCl_{5(g)} \longleftrightarrow PCl_{3(g)} + Cl_{2(g)}$

$PCl_5$,$PCl_3$,and $Cl_2$ are at equilibrium at $500 \ K$ with concentrations $[PCl_3] = 1.59 \ M$,$[Cl_2] = 1.59 \ M$,and $[PCl_5] = 1.41 \ M$. Calculate $K_c$ for the reaction:
$PCl_5 \rightleftharpoons PCl_3 + Cl_2$

The equilibrium constant of the following reaction is $0.5$. $CO_{(g)} + 2H_{2(g)} \rightleftharpoons CH_3OH_{(g)}$. At equilibrium,$[CO] = 0.18 \ mol \ L^{-1}$ and $[H_2] = 0.22 \ mol \ L^{-1}$. Calculate the concentration of $CH_3OH$.