Three point charges $1 \mathrm{C},-2 \mathrm{C}$ and $-2 \mathrm{C}$ are placed at the vertices of an equilateral triangle of side 1 metre. The work done by an external force to increase the separation of the charges to 2 metre in joule is ( $\varepsilon_0=$ permittivity of air)

• A

  $\frac{1}{4 \pi \varepsilon_0}$
• B

  $\frac{1}{8 \pi \varepsilon_0}$
• C

  $\frac{1}{16 \pi \varepsilon_0}$
• Correct answer
  D

  $zero$

Hence, the correct answer is option: 'D'.