Which equation represents the second ionization energy of magnesium? Choose one:
a. Mg+ (g) + e- → Mg (g)
b. Mg+ (g) → Mg2+ (g) + e-
c. Mg (g) → Mg+ (g) + e-
d. Mg(g) → Mg2+ + 2e-
e. Mg(g) + e- → Mg- (g)
f. Mg2+ (g) +2e- → Mg (g)