Four charges are placed on corners of a square ABCD, A = Q, B = -2Q, C = +2Q & D = -Q having side of 5cm. If Q is one microcoulomb, then electric field intensity at centre will be

a) 1.02 x 10⁷ N / C upwards

b) 2.04 x 10⁷ N / C downwards

c) 2.04 x 10⁷ N / C upwards

d) 1.02 x 10⁷ N / C downwards