Question

Why the Torque on Both side Of The Dipole Placed In Uniform electric Field Is Not Zero ?

Answer 1

In a uniform electric field the dipole rotates and tends to align itself in the direction of the dipole moment.Hence we find the dipole moving.
Torque ι = PE sinФ
Where PE is the length of the dipole and Ф is the angle to which the dipole is aligned to the electric field.
The two forces that is created are equal and opposite in nature.Thus torque remains in the dipole.
Force becomes zero only when the two opposite forces in the dipole balances each other and the dipole comes to rest..

Answer 2

When an electric  dipole is placed in uniform electric field, two equal and unlike parallel forces act on either side of the dipole. This gives rise to a torque on the dipole. (Torque = either force x perpendicular distance between the two forces) 

Since, the two forces are equal and unlike ( one opposite to the direction of electric field and the other in the direction of electric field ) , the net force on the dipole is zero but not its torque.