Two charges \(q,\) \(-q\) are placed at the two ends of the hypotenuse of an isosceles right-angled triangle, the smaller sides being of length, \(a.\) A dipole of dipole moment \(p\) is placed at the right-angled vertex with its axis pointing towards the positive charge, \(q.\) The torque acting on the dipole is:
1. \(\dfrac{kpq}{a^2}\)

2. zero

3. \(\dfrac{2kpq}{a^2}\)

4. \(\dfrac{\sqrt{5}kpq}{a^2}\)