2 NaI (aq) + Na₂SO₄ (aq) + H₂O (l) → Na₂SO₃ (aq) + I₂ (s) + 2 NaOH (aq)

This is an oxidation-reduction (redox) reaction:

Na₂SO₄ is an oxidizing agent, NaI is a reducing agent.

Reactants:

• NaI
  • Names: Sodium iodide , Sodium iodide (anhydrous) , NaI , Sodium monoiodide
  • Appearance: White solid | deliquescent ; Colourless-to-white hygroscopic crystals or white powder. turns brown on exposure to air
• Na₂SO₄
  • Names: Sodium sulfate , Sodium sulphate , Sulfate of sodium ... show moreThenardite (mineral) , Glauber's salt (decahydrate) , Sal mirabilis (decahydrate) , Mirabilite (decahydrate mineral) , Disodium sulfate , Anhydrous sodium sulfate , Sodium sulfate anhydrous , Sodium sulfate, anhydrous , Sodium sulphate anhydrous , Sodium sulphate, anhydrous , Sulfuric acid disodium salt, anhydrous , Disodium sulphate , Salt cake , Na2SO4 , Sulfuric acid disodium salt show less
  • Appearance: White crystalline solid | hygroscopic ; White hygroscopic solid in various forms
• H₂O – Water, oxidane
  • Other names: Water (H2O) , Hydrogen hydroxide (HH or HOH) , Hydrogen oxide ... show moreDihydrogen monoxide (DHMO) (systematic name) , Hydrogen monoxide , Dihydrogen oxide , Hydric acid , Hydrohydroxic acid , Hydroxic acid , Hydrol , Μ-oxido dihydrogen , Κ1-hydroxyl hydrogen(0) show less
  • Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas

Products:

• Na₂SO₃ – Sodium sulfite
  • Other names: Sodium sulphite , Hypo clear (photography) , E221 ... show moreNa2SO3 , Anhydrous sodium sulfite , Sodium sulfite anhydrous , Sulfurous acid, disodium salt , Dried sodium sulfite , Disodium sulfite show less
  • Appearance: White solid ; White crystals or powder
• I₂
  • Names: Iodine , Jod , Iode ... show moreIodio , Yodo , Iodine crystals , Molecular iodine show less
  • Appearance: Bluish black or dark purple crystals with pungent odour ; Violet solid with a sharp, characteristic odor.
• NaOH
  • Names: Sodium hydroxide , Caustic soda , Lye ... show moreSoda lye , Sodium hydrate , NaOH , White caustic , Lye [Sodium hydroxide] show less
  • Appearance: White, waxy, opaque crystals ; White hygroscopic solid in various forms ; Colorless to white, odorless solid (flakes, beads, granular form).