Why are $H_2SO_4$ and $CaCl_2$, not suitable for drying ammonia gas? They

Analyze the question: Ammonia gas is being dried (water vapour removed). We're asked why concentrated H₂SO₄ and anhydrous CaCl₂ cannot be used as the drying agents.

Concept: A drying agent must remove water without reacting with the gas being dried. Ammonia (NH₃) is a basic gas, and it is also able to form complexes with certain salts.

Step-by-step solution:

1. H₂SO₄ and NH₃: Ammonia is a base and sulphuric acid is an acid, so they undergo neutralisation: 2NH₃ + H₂SO₄ → (NH₄)₂SO₄ The ammonia is used up, forming ammonium sulphate.

2. CaCl₂ and NH₃: Anhydrous calcium chloride combines with ammonia to form an addition compound (a complex): CaCl₂ + 8NH₃ → CaCl₂·8NH₃ Again, the ammonia is absorbed and lost.

3. Conclusion: In both cases the drying agent reacts with the gas, so the ammonia would not be collected. Poisonous (A), pollute (B) and corrosive (C) are not the real reason. Corrosiveness is true of H₂SO₄ but not relevant to CaCl₂, and it is not why they are unsuitable.

Correct answer: D, react with the gas

Tip: Match the drying agent to the gas type:

• Basic gas (NH₃) → use quicklime (CaO), which is also basic and doesn't react with it.
• Acidic gases (HCl, SO₂, CO₂) → conc. H₂SO₄ is fine (HCl, SO₂, CO₂ don't react with it).
• Remember: "NH₃ hates acids and CaCl₂, so CaO is its friend."