Two charges, each equal to q, are kept at $x = − a$ and $x = a$ on the x−axis. A particle of mass $m$ and charge $q_0 = \large\frac{q}{2}$ is placed at the origin. If charge $q_0$ is given a small displacement $(y << a)$along the y−axis, the net force acting on the particle is proportional to :

Question

$\begin{array}{1 1} (1) y \\ (2)-y \\ (3) \large\frac{1}{y} \\ (4) \large\frac{-1}{y} \end {array}$