1. What is the oxidation number of Mn in KMnO₄ in acidic medium?

題解： In acidic medium, KMnO₄ is reduced to Mn²⁺. Mn changes from +7 to +2. Therefore, the oxidation number of Mn in KMnO₄ is +7. This is a common Redox reaction tested in DSE.

2. Explain why the equilibrium constant Kc for the Haber process is temperature dependent.

題解： The Haber process (N₂ + 3H₂ ⇌ 2NH₃) is exothermic. According to Le Chatelier’s Principle, increasing temperature shifts equilibrium to the left, decreasing Kc. This demonstrates the relationship between enthalpy change and equilibrium position.

3. Calculate the pH of 0.01M HCl solution.

題解： HCl is a strong acid, so [H⁺] = 0.01M. pH = -log(0.01) = 2. This tests understanding of pH calculation and strong acid behaviour.

4. Name the functional group in CH₃CH₂CHO and state one chemical test.

題解： The functional group is aldehyde. It gives a silver mirror with Tollens’ reagent (ammoniacal silver nitrate). This is a key Organic Chemistry identification question.

5. What is the role of a catalyst in a chemical reaction?

題解： A catalyst provides an alternative reaction pathway with lower activation energy, increasing the rate of reaction without being consumed. It does not affect the equilibrium position or yield.