d
\(\mathop {2{N_2}}\limits^0  + \mathop {{O_2}}\limits^{0{\mkern 1mu} {\mkern 1mu} }  \to \mathop {\mathop {2N}\limits^{{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu}  + 2} {\mkern 1mu} \mathop {{\text{ }}O}\limits^{ - 2} }\limits^{\mkern 1mu}  \) 

Here \(O.N.\) of \(N\) increases from \(O\) in \({N_2}\) to \(+2 \) in \(NO, 2- \) and that of decreased from \(O\) in \({O_2}\) to \(-2 \) in \(O,\)  therefore, it is a redox reaction.