first you need to find the moles of NO2:
Mr NO2 = 46
Mass NO2 = 14
moles = mass/mr
= 14/46
= 0.304
this value is for a ratio of 4 since there are 4 NO2
there is only 1 O2 therefore we divide by 4
0.304/4 = 0.0761
mass O2 = moles x mr
= 0.0761 x 32 = 2.43
