Board-style MCQs and past-paper questions in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved numericals are at the bottom.
Multiple-choice questions
Solved numericals & self-assessment (past papers)
Neutrons, protons & electrons in ⁴⁰₂₀Ca²⁺
Z = 20 → 20 protons. A = 40 → neutrons = A − Z = 40 − 20 = 20 neutrons
The 2+ ion has lost 2 electrons → 20 − 2 = 18 electrons
Relative atomic mass of boron
Boron is 19.6% ¹⁰B and 80.4% ¹¹B.
A_r = (19.6×10 + 80.4×11)/100 = (196 + 884.4)/100 = 10.8 a.m.u
Energy of a photon of wavelength 600 nm
E = hc/λ = (6.63×10⁻³⁴ × 3×10⁸) / (600×10⁻⁹)
= (1.989×10⁻²⁵) / (6×10⁻⁷) = 3.315 × 10⁻¹⁹ J
Bohr radius & energy of the n = 3 orbit of hydrogen
rₙ = 0.529 × n² Å = 0.529 × 9 = 4.76 Å
Eₙ = −1312/n² = −1312/9 = −145.8 kJ·mol⁻¹
Electronic configuration of Fe and Fe³⁺ (Z = 26)
Fe: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s² = [Ar] 3d⁶ 4s²
Fe³⁺ loses 4s² then one 3d → [Ar] 3d⁵ (a stable half-filled d).