Answer : The correct option is a) Loses electrons and loses potential energy.
Explanation :
Reducing agent : In a redox reaction, it is oxidized by the loss of electrons and by the loses of potential energy. It is also called as electron donor.
Reducing agent reduces others by loss of electron and its oxidation state increases.
For example : Sodium is a reducing agent and itself oxidized as follows,
Therefore, the molecule that function as a reducing agent in a redox reaction is loses electrons and loses potential energy.