C-06-Q127mediumsingle_mcqIn 2Mg(NO3)2→Δ2MgO+?+O2\mathrm{2Mg(NO_3)_2 \xrightarrow{\Delta} 2MgO + ? + O_2}2Mg(NO3)2Δ2MgO+?+O2, the missing product is—aN2\mathrm{N_2}N2b4NO2\mathrm{4NO_2}4NO2