Three point charges+ q, - 2q and+ q are placed at points (x = 0, y = a, z = 0), (x = 0, y = 0, z = 0) and (x = a, y = 0, z = 0), respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are :

• A

  $\sqrt{2}$qa along + y direction

• B

  $\sqrt{2}$qa along the line joining points

  (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0)

• C

  qa along the line joining points

  (x = 0, y = 0, z = 0)
  and (x = a, y = a, z = 0)

• D

  $\sqrt{2}$qa along + x direction