Sulfur, selenium and tellurium burn in air to form SO₂.SeO₂ and TeO₂ . The dioxide molecules contain pπ–pπ bonds which become weaker with increase in atomic number because of the increase in the bond length.

(a) Sulfur dioxide, SO₂ is a gas at room temperature and exists as individual molecules even in the solid state. Its molecule has bent structure and is a resonance hybrid of the following canonical structures.

SO₂ is acidic in nature and also called the anhydride of sulfurous acid. It can act as reducing and oxidizing agent. SO₂ also acts as a bleaching agent in the presence of moisture, but in contrast to Cl₂ , its bleaching action is temporary.

SO₂ + 2H₂O ————> H₂SO₄ + 2[H]

Coloring matter +2[H] ? Colorless compound

Hence, SO₂ bleaches due to reduction and the bleaching action is temporary.

(b) Selenium dioxide, SeO₂ is a solid with polymeric zig-zag structure at room temperature however it exist as discrete molecules in the gaseous phase.

(c) Tellurium dioxide, TeO₂ is also a solid with polymeric zig-zag structure at room temperature very similar to that of selenium dioxide.