During the formation of the dimer $N_2O_4$ from two molecules of $NO_2$,what happens to the unpaired electron on the nitrogen atom of each $NO_2$ molecule?

• A
  $A$ weak $N-N$ bond is formed,two $N-O$ bonds become equal,and the other two $N-O$ bonds become unequal.
• B
  $A$ weak $N-N$ bond is formed and all four $N-O$ bonds become equal.
• C
  $A$ weak $N-N$ bond is formed and all four $N-O$ bonds become unequal.
• D
  $A$ strong $N-N$ bond is formed and all four $N-O$ bonds become equal.