At what change in Gibbs free energy $(\Delta G)$ does a reaction reach equilibrium?

Explain the equilibrium when sublimation of solid takes place in a closed vessel.

For the reaction ${H_2} + {I_2} \rightleftharpoons 2HI$ at $721 \ K$,the value of the equilibrium constant is $50$. If $0.5 \ mol$ of each of ${H_2}$ and ${I_2}$ are added to the system,the value of the equilibrium constant will be .............

The equilibrium constant in a reversible reaction at a given temperature:

If the concentration of reactants is increased by $x$ times,the equilibrium constant $K$ will become ................

Which of the following statements is correct regarding the equilibrium constant $(K)$?