The angular momentum of planet about sun is constant.
ie $mvr \sin \theta $= constant
where $\theta$ is the angle between radius vector and velocity vector
At P and Q $\theta=90^{\circ}$
and $m-$ mass of planet is constant.
$\therefore \; vr= constant$
$\large\frac{v_1}{v_2}=\frac{r_2}{r_1}$
Hence b is the correct answer.