Point charges q₁ = -4.20 nc and q₂ = 4.20 nc are separated by a distance of 3.20 mm, forming an electric dipole. What is the magnitude of the electric field at a point on the dipole's axis?
a) 0 N/C
b) 4.20 × 10⁶ N/C
c) 1.31 × 10⁶ N/C
d) 2.62 × 10⁶ N/C