Sodium sulfite is used to remove permanganate stains because it undergoes a redox reaction with potassium permanganate. Here's the chemical reaction that takes place:

2 KMnO₄ + 5 Na₂SO₃ + H₂O → K₂SO₄ + 2 MnSO₄ + 5 NaHSO₄

In this reaction, potassium permanganate (KMnO₄), which is the oxidizing agent, gets reduced to manganese sulfate (MnSO₄), while sodium sulfite (Na₂SO₃) gets oxidized to sodium bisulfite (NaHSO₄). The by-products of the reaction are potassium sulfate (K₂SO₄) and water (H₂O).

During the reaction, the purple color of potassium permanganate gradually disappears, indicating that the stain is being removed. The colorless products formed in the reaction are water-soluble and can be easily washed away.

When using sodium sulfite to remove permanganate stains, it's important to follow safety precautions and handle the chemicals with care. Always wear protective gloves and ensure adequate ventilation to prevent inhalation of fumes. Use the sodium sulfite solution as per the recommended instructions, and thoroughly rinse the stained area with water afterward.