The Reaction That Occurs in a Hydrogen Fuel Cell, Shown

The reaction that occurs in a hydrogen fuel cell, shown below, is exothermic. According to the Conservation of Energy, the reverse reaction, called electrolysis, 2H₂ + O₂ → 2H₂O hydrogen fuel cell
2H₂O → 2H₂ + O₂ electrolysis

A) is also exothermic.
B) is endothermic.
C) does not involve energy.
D) has an energy change of zero.
E) involves energy in some way, but it is impossible to determine how.