standard enthalpy

The standard enthalpy change for which of the following processes corresponds to the standard enthalpy of formation of solid rubidium chloride?
A) Rb(s) + 1/2 Cl2(s) ? RbCl(s)
B) Rb(g) + 1/2 Cl2(g) ? RbCl(g)
C) Rb(g) + Cl(g) ? RbCl(s)
D) Rb(s) + 1/2Cl2(g) ? RbCl(s)
E) Rb(s) + 1/2 Cl2(s) ? RbCl(g)