Answer
Choice (b)
Work Step by Step
From conservation energy law we could get the charge by
\begin{gather}
K =U \\
K =k \frac{q_2 q_1}{r} \\
q_2 =\frac{r K }{k q_1}\\
q_2 = \frac{r K }{k\,2e }\\
q_2 =\frac{\left(10 \times 10^{-15} \mathrm{m}\right)\left(3.0 \times 10^{6} \mathrm{eV} \times 1.6 \times 10^{-19} \mathrm{J} \right)}{2e\left(9.0 \times 10^{9} \mathrm{N} \cdot \mathrm{m}^{2} / \mathrm{C}^{2}\right)}\\
q_2 = 1.66 \times 10^{-18} \,\text{C}
\end{gather}
To get the charge in $e$, we divide the charge by $1.6 \times 10^{-19}$
$$q_2 = \dfrac{1.66 \times 10^{-18} \,\text{C} }{1.6 \times 10^{-19}} \approx 11e $$
The answer is choice (b)
