 Solution

At fixed temperature, a phase's Gibbs free energy satisfies $\mathrm{d}G=V\mathrm{d}p$. For the metallic-minus-molecular difference,Increasing pressure favors the smaller-volume metallic phase. With a pressure-independent volume approximation, $\Delta G(p)\simeq \Delta G(p_0)+(p-p_0)\Delta V$, so pressure can overcome an initially positive free-energy difference. The volume comparison explains the direction of stabilization; it does not by itself determine the transition pressure or the electronic origin of metallic bonding.