Free Shape of Ionic Crystals MCQs with Answers

1. The unit cell of sodium chloride is

• A. simple cubic
• B. hexagonal
• C. body centred cubic
• D. face centred cubic

Explanation: Sodium chloride crystallises in a face centred cubic arrangement in which each sodium ion is surrounded octahedrally by six chloride ions and each chloride by six sodium ions, giving a coordination number of six for both. Caesium chloride, whose larger cation allows eight neighbours, adopts a body centred arrangement instead. The unit cell is simply the smallest repeating block from which the whole lattice can be built.

2. The coordination number of an ion in a crystal lattice is

• A. the number of oppositely charged ions immediately surrounding it
• B. the charge on the ion
• C. the number of unit cells it belongs to
• D. the number of electrons it has lost or gained

Explanation: Coordination number counts the nearest neighbours of opposite charge, so it is six in sodium chloride and eight in caesium chloride, the difference arising from the relative sizes of the ions. A larger cation can accommodate more anions around it before they begin to touch each other. The number of electrons transferred determines the charge, which is a separate quantity.