According to Gauss’s law for electric field, the total flux crossing the closed surface is equal to the charge enclosed by that surface

The electric flux through the closed surface is,

$ψ= ∮_s \bar{D} .d \bar{s}$

The charge can be expressed in terms of $ρ_v$ as:

$Q_{enclosed}= ∫_v ρ_v.dv$

The …