Is a square a rhombus

Yes. A rhombus is a special form of parallelogram, and it is a parallelogram which has four equal sides. If the rhombus happens to have its sides at right angles, it's a square, which is a special form of rhombus, which is, in turn, a special form of a parallelogram, which is a special form of a quadrilateral, which is a four-sided planar polygon.
False Apex