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 system are:

• A
  Magnitude $\sqrt{2}qa$ in the direction of the line joining $(0, 0, 0)$ and $(a, a, 0)$
• B
  Magnitude $\sqrt{2}qa$ in the direction of the line joining $(a, a, 0)$ and $(0, 0, 0)$
• C
  Magnitude $qa$ in the direction of the line joining $(0, 0, 0)$ and $(a, a, 0)$
• D
  Magnitude $2qa$ in the direction of the line joining $(0, 0, 0)$ and $(a, a, 0)$