Board-style MCQs and past-paper questions in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved questions & self-assessment (past papers)
Why does ionization energy increase across a period but decrease down a group?
Across a period, nuclear charge rises while electrons fill the same shell, so the radius shrinks and the valence electron is held more tightly → IE increases.
Down a group, each period adds a new shell; the valence electron is farther out and well shielded, so it is removed more easily → IE decreases.
State the inert-pair effect and give one example.
In the heavier p-block elements the outer ns² pair resists bonding, so the lower (group−2) oxidation state becomes more stable down the group.
Example: in Group IVA, Pb²⁺ is more stable than Pb⁴⁺ (and Tl⁺ > Tl³⁺ in Group IIIA).
Outline the Contact process and justify its conditions.
Stage 1: S + O₂ → SO₂. Stage 2: 2SO₂ + O₂ ⇌ 2SO₃ (exothermic, catalyst V₂O₅). Stage 3: SO₃ + H₂SO₄ → oleum (H₂S₂O₇), then + H₂O → 2H₂SO₄.
Conditions: ~450 °C (compromise between yield and rate), 1–2 atm (forward side has fewer gas moles, so low P already gives ~98% yield), excess air pushes equilibrium forward → high yield of H₂SO₄.