The equilibrium constant for the reaction $H_{2(g)} + I_{2(g)} \leftrightharpoons 2HI_{(g)}$ is $64$ at a certain temperature. The equilibrium concentrations of $H_2$ and $HI$ are $2\;mol/L$ and $16\; mol/L$ respectively. What is the equilibrium concentrations (in $mol/L$) of $I_2$ ?
