The table shows diagonal properties of four quadrilaterals P, Q, R and S (all parallelograms). Which one is a rhombus but not a square?

A rhombus has perpendicular diagonals; if they were also equal it would be a square. R has perpendicular but unequal diagonals. P (both) is a square, Q (equal only) a rectangle, S (neither) a general parallelogram.