Sulfur dioxide gets reacts with water vapor to produce aqueous hydrogen sulfite.

SO₂ +  H₂O → HSO₃⁻ + H⁺

Explanation:

Assuming, you want to know the final balanced equation of this reaction, which is in words.

Sulfur dioxide reacts with water vapor to produce aqueous hydrogen sulfite and H⁺ ions(acidic).

Sulfur dioxide: SO₂(g)

Water vapor: H₂O(g)

Hydrogen sulfite: HSO₃⁻(aq)

Before putting them in the equation, check for each element's oxidation state to identify the nature of the reaction.

OS of S in SO₂ is +4, and in HSO₃⁻ is also +4.

OS of H and O remain +1 and -2, respectively.

SO₂ +  H₂O → HSO₃⁻ + H⁺

This further reacts to form sulfur trioxide (SO₃) gas, which is main cause for acid rain, as this reacts with water vapor in atmosphere to form sulfuric acid.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.