d
As mass of proton $>>>$ mass of positron so initial acceleration of positron is much larger than proton. Therefore position reach far away in very short time as compare to proton.
$2 \mathrm{K}_{\mathrm{e}^{+}}=\left(\frac{4 \mathrm{kq}^{2}}{\mathrm{a}}+\frac{2 \mathrm{kq}^{2}}{\mathrm{a} \sqrt{2}}\right)-\frac{\mathrm{kq}^{2}}{\mathrm{a} \sqrt{2}}$
$ \Rightarrow {{\rm{K}}_{{{\rm{e}}^ + }}} = \frac{{{{\rm{q}}^2}}}{{2\pi { \in _0}{\rm{a}}}}\left( {1 + \frac{1}{{4\sqrt 2 }}} \right)$ and
$2{{\rm{K}}_{\rm{p}}} = \frac{{{\rm{k}}{{\rm{q}}^2}}}{{{\rm{a}}\sqrt 2 }} - 0 \Rightarrow {{\rm{K}}_{\rm{p}}} = \frac{{{{\rm{q}}^2}}}{{8\sqrt 2 \pi { \in _0}{\rm{a}}}}$
