Consider the following conditions on a parallelogram $P Q R S$, labelled anticlockwise:
I length of $P Q =$ length of $Q R$\\
II The diagonal $P R$ intersects the diagonal $Q S$ at right angles\\
III $\angle P Q R = \angle Q R S$\\
Which of these conditions is/are individually sufficient for the parallelogram $P Q R S$ to be a square?