Answer: (B)
A square and a rhombus of the same area are not always similar, as their angles differ (a square has all 90° angles, a rhombus need not).
Similarity requires both equal corresponding angles AND proportional sides. A rhombus has equal sides but its angles can vary, so it is not always similar to a square. The other three statements are correct: congruent figures are always similar (ratio 1:1); two equilateral triangles always have 60°-60°-60°; similar triangles need not be congruent. Examiners expect you to identify the false statement and briefly justify.