Board-style MCQs and reasoning questions in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved reasoning & self-assessment (past papers)
Atoms per unit cell for SC, BCC and FCC
Simple cubic: 8 corners × ⅛ = 1
Body-centred: (8 × ⅛) + 1 centre = 2
Face-centred: (8 × ⅛) + (6 × ½) = 4
Why is graphite a conductor but diamond an insulator?
In diamond every carbon is sp³ and uses all 4 valence electrons in covalent bonds → no free electrons.
In graphite each carbon is sp² (3 bonds), leaving one delocalised electron per atom that can move along the layers → graphite conducts.
Why does NaCl have a sharp melting point but glass does not?
NaCl is crystalline — all the ionic bonds are identical, so they break at one temperature (sharp m.p.).
Glass is amorphous — a range of bond strengths, so it softens gradually over a range → no sharp melting point.
Classify: diamond, NaCl, dry ice (CO₂), copper
Diamond → covalent (network) · NaCl → ionic · dry ice → molecular · copper → metallic
Why does MgO have a higher melting point than NaCl?
MgO has ions of charge 2+ and 2− (vs 1+/1− in NaCl) and smaller ions → much greater lattice energy → higher melting point.