Among the given oxides of nitrogen; \( \mathrm{N_2O} \), \( \mathrm{N_2O_3} \), \( \mathrm{N_2O_4} \) and \( \mathrm{N_2O_5} \), the number of compound/(s) having \( \mathrm{N-N} \) bond is:
\( 1 \)
\( 2 \)
\( 3 \)
\( 4 \)