The equilibrium, solid ⇌ liquid ⇌ gas will shift in the forward direction when

Explanation

The equilibrium involving solid, liquid, and gas phases described here is an endothermic process. Raising the temperature provides the energy needed for the solid to transition into liquid and subsequently into gas, shifting the equilibrium to the right. This supports the forward direction of the reaction. In contrast, keeping the temperature constant or lowering it does not provide the energy required for the endothermic process, hence the equilibrium remains unchanged or shifts left. Pressure changes have no significant effect on this solid-liquid-gas equilibrium, as they primarily impact equilibria involving gases with differing moles.