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

1. A
   $qa$ along $+y$ direction
2. B
   $\sqrt{2}qa$ along the line joining points $(0,0,0)$ and $(a,a,0)$
3. C
   $qa$ along the line joining points $(0,0,0)$ and $(a,a,0)$
4. D
   $qa$ along $+x$ direction