In the following reaction,$3CuO + 2NH_3 \to N_2 + 3H_2O + 3Cu$,what happens during the conversion of $NH_3$ to $N_2$?

• A
  Per mole of $N_2$,$6$ electrons are lost.
• B
  Per mole of $N_2$,$3$ electrons are lost.
• C
  Per mole of $N_2$,$7$ electrons are gained.
• D
  Per mole of $N_2$,$3$ electrons are gained.