Redox Reactions

BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl is a double displacement reaction with no change in oxidation states, so it is not a redox reaction. In the other options, there is a clear change in oxidation numbers indicating redox processes.

Mohr’s salt (ferrous ammonium sulphate) is commonly dissolved in slightly acidic solution (using dilute H₂SO₄) to prevent oxidation and hydrolysis of Fe²⁺ ions. The acidic medium suppresses Fe²⁺→Fe³⁺ conversion and formation of insoluble iron hydroxides, ensuring the stable, clear solution of Mohr’s salt.

Mohr’s salt (ferrous ammonium sulphate) is commonly dissolved in slightly acidic solution (using dilute H₂SO₄) to prevent oxidation and hydrolysis of Fe²⁺ ions. The acidic medium suppresses Fe²⁺→Fe³⁺ conversion and formation of insoluble iron hydroxides, ensuring the stable, clear solution of Mohr’s salt.