$A$ fundamental particle of mass $m$ and charge $+e$ is projected towards a much heavier charged particle of charge $+Ze$,where $Z > 0$. The distance of closest approach of the incident particle is ........

• A
  $\frac{Ze^2}{2\pi \varepsilon_0 mv^2}$
• B
  $\frac{Ze}{4\pi \varepsilon_0 mv^2}$
• C
  $\frac{Ze^2}{8\pi \varepsilon_0 mv^2}$
• D
  $\frac{Ze}{8\pi \varepsilon_0 mv^2}$