Two identical charges each having a charge $+Q$ are fixed at a separation $2 a.$ A small particle $P$ having a charge of magnitude $q$ is placed midway between them. Now, $P$ is given a displacement $\Delta (\ll a)$, such that it undergoes simple harmonic motion. For this, We have the following $(q,\Delta )$ combinations.

$q is+ve$ then there will be net repulsive force which will send the charge particle back to its original position so it will be an S.H.M.

$\mathrm{q} is-ve$ then there will be net attractive force which will send the charge particle back to its original position so it will be an S.H.M.

The correct answer is 1,3