Answer:

In ∆ ABC, P and Q are mid points of AB and AC respectively.

So, PQ || BC, and PQ =

???????? …(1)

Similarly, in ∆ADC, …(2)

Now, in ∆BCD, SR =

???????? …(3)

In ∆ABD,

With (1), (2), (3), and (4).

PQ = QR = SR = PS

All sides are equal

Therefore, PQRS is a rhombus.