The equilibrium $\mathrm{H}{}_2(\mathrm{g})+\mathrm{I}{}_2(\mathrm{g})\rightleftharpoons 2\mathrm{HI}(\mathrm{g})$ is established in a closed vessel. If the volume of the vessel is reduced at constant temperature, the amount of $\mathrm{HI}$

1. Aincreases, as pressure favours the product
2. Bdecreases, as pressure favours the reactants
3. Cincreases, as $K_c$ increases
4. Dremains unchanged, as $\Delta n_g=0$