In the situation shown in the diagram, the magnitude of $Q$ is such that $r \gg a$. The net force on the free charge $-q$ and the net torque on it about point $O$ at the instant shown are, respectively. $p = 2aQ$ is the dipole moment.
$-\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^2} \hat{k}, -\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^3} \hat{i}$
$\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^3} \hat{i}, +\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^2} \hat{k}$
$\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^3} \hat{i}, -\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^3} \hat{k}$
$\frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^2} \hat{k}, \frac{1}{4 \pi \varepsilon_0} \frac{pq}{r^3} \hat{i}$
