Hardness of water is mainly caused by the presence of dissolved salts of: MCQ with Answer and Explanation

Explanation:
The Contact process produces sulphuric acid: S + O₂ → SO₂; 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst); SO₃ + H₂SO₄ → H₂S₂O₇ (oleum); H₂S₂O₇ + H₂O → 2H₂SO₄. Haber process for NH₃, Ostwald for HNO₃, Solvay for Na₂CO₃.

Explanation:
Sodium carbonate (Na₂CO₃), also called soda ash, is a key ingredient in glass manufacturing. It lowers the melting point of silica (SiO₂) and provides sodium oxide. The glass batch consists of sand (SiO₂), soda ash (Na₂CO₃), and limestone (CaCO₃). Sodium chloride is table salt, potassium nitrate used in gunpowder, ammonium chloride in batteries/leclanche cells.

Explanation:
Petroleum originates from microscopic marine organisms (plankton) that sank to the seabed and were transformed by heat/pressure over millions of years. Coal is from land plants.