Identify the compound whose solubility decreases with increasing temperature.

Answer is: Na₂SO₄ (sodium sulfate).

The solubility of sodium sulfate increases up to 32.38°C and than decreases at higher temperatures, the solubility becomes almost independent of temperature.

At 32.38°C it releases of crystal water and melting of the hydrated salt.

Sodium sulfate is the white, inorganic compound.

Sodium sulfate is highly soluble in water.