7.5g of a gas occupies 5.6 litres as STP.  The gas is

5.6 lit at STP weights 7.5 gms

 22.4 lit at STP weights $=\frac{22.4\times 7.5}{5.6}$

= 30 gms

 $\therefore$ mol. wt of gas = 30

$\therefore$  NO has mol. wt 30.