Four point charges -Q, -q, 2q and 2Q are placed, one at each comer of the square. The relation between Q and q for which the potential at the centre of the square is zero is:

• A

  Q = q

• B

  $\mathrm{Q}=\frac{1}{\mathrm{q}}$

• C

  Q = -q

• D

  $\mathrm{Q}=-\frac{1}{\mathrm{q}}$