From the figure given, it is seen that the electric field is not uniform. Electric field is decreasing from left to right direction. This means that electric field is stronger in the left side as compared to the right side. Now, a dipole is kept in this field.

We know that there is force acting on the positive charge in the direction of applied electric field while there is force acting on the negative charge in the opposite direction of applied electric field.

The figure below shows the direction of the force (F_+q and F_-q) on the negative as well as positive charge due to the non-uniform field.

The force on the negative charge is greater than the force on the positive charge due to the presence of strong electric field around negative charge. Therefore, the dipole as a whole is experiencing net force on the left side.