Consider the charge configuration and a spherical Gaussian surface as shown in the figure. When calculating the flux of the electric field over the spherical surface, the electric field will be due to :

all the charges

At any point over the spherical Gaussian surface, net electric field is the vector sum of electric field due to +q₁, –q₁ and q₂. Don’t confuse with the electric flux which is zero (net) passing over the Gaussian surface as the net charge enclosing the surface is zero. Hence, the correct option is (c).