Which are heavier than dry air? 

To address this, we must first understand that dry air is just air devoid of any moisture or water molecule. Dry air has a molar mass of approximately 28.97 g/mol. Knowing the molar masses of wet air, SO₂, Cl₂, and O₂ is necessary to solve this. The heavier gases are those whose molar masses exceed that of dry air.

We are aware that dry air is air devoid of any water molecules or moisture. Dry air has a molar mass of approximately 28.97 g/mol.
The definition of moist air is "air that includes water molecules or moisture." The molar mass of moist air is therefore equal to the sum of the molar masses of dry air and water.
In comparison to dry air, moist air has a higher molar mass of 46.97 g/mol.
Dry air is lighter than damp air as a result. Thus, choice (A) is the right one.

Sulfur dioxide gas is known as SO₂. Sulfur dioxide gas has a higher molar mass than dry air (64.06 g/mol) than that of air.
SO2 is hence heavier than dry air. Thus, choice (B) is the right one.
chlorine gas, or Cl₂. Chlorine gas has a higher molar mass per mole (70.90 g/mol) than dry air.
Cl₂ is hence heavier than dry air. The correct answer is (C), thus.
Oxygen gas is O₂. The molar mass of oxygen gas is larger than that of dry air at 31.98 g/mol.
O₂ is therefore heavier than dry air. Option (D) is incorrect as a result.

Thus, gases heavier than dry air are moist air, SO₂ and Cl₂.

Thus, the correct options is D.