Question

When is a parallelogram is a rhombus ?

Answer 1

When all of its sides are the same length.

Answer 2

A parallelogram is a rhombus when one of the following conditions is done:
1. All sides of the parallelogram are equal to each other.
2. The diagonals of the parallelogram intersect at a right angle (90°).
3. The diagonals of the parallelogram are the bisectors of its angles.

I hope this helps.