A, according to the image, when molecule B is at point P (x=x2), the molecular potential energy is the smallest, at this time, the molecule is in an equilibrium position, the molecular attraction is equal to the molecular repulsion, the resultant force is zero, and the acceleration is zero, so A is wrong.

B, according to the image, the molecular potential energy of molecule B at point Q is zero, which is greater than that at point P, so the molecular potential energy at point Q is not the minimum, so B is wrong;

C when molecule b is at q (x=x 1), the intermolecular distance is less than the equilibrium distance, and the resultant force of molecular attraction and molecular repulsion is repulsion. At point Q, the molecule is not in equilibrium, so C is wrong;

D when molecule b is at point p (x=x2), the molecular potential energy is the smallest. According to the law of conservation of energy, kinetic energy of molecules is the largest, so D is correct;

So choose D.