7.5gms of a gas occupy 5.6 litres of volume at STP.The gas is:

Given Mass of gas = 7.5 g

Volume = 5.6L

At STP = 1 mol.of substance occupies 22.4L of volume.

Therefore for the above gas to acquire 22.4 lit volume its mass should be 22.4/5.6 x 7.5 = 30g = mol. Wt of gas.

Since no element with at mass 30 exists it may be a hetero-atomic gas most probably NO