Gauss's law is usualy written as:

∫Φ_E = E * dA = qencl / ε0

what does qencl refers in Guass's law?

O the net charge inside the closed surface

O the charge residing on insulators inside the closed surface

O all the charge in the physical system

O any charge inside the closed surface that is arranged symmetrically

(a) the net charge inside the closed surface.

Explanation:

In Gauss' Law, Qencl refers to the net charge inside the Gaussian surface. This surface is usually taken as a symmetric geometric surface, but this is merely for simplicity. Gauss' Law holds for any closed surface. Inside this surface there can be insulators as well as conductors. Regardless of the geometry or the materials inside, Qencl refers to the net charge inside the closed surface. The charge outside the surface is irrelevant for Gauss' Law, therefore all the charge in the physical system is not included in Gauss' Law.