Question on Bleaching Action

Why is the bleaching action of SO₂ temporary while the bleaching action of CaOCl₂ (bleaching powder) permanent?

Answer:

The bleaching action of SO₂ is due to its reducing property while that of bleaching powder is due to is oxidizing property. The article bleached by SO₂ gets reduced while that getting bleached by bleaching powder gets oxidized. The article that gets reduced by the bleaching action of SO₂ can again be oxidized when it is exposed to air. So, the bleaching action of SO₂ is temporary.