Obtain Gauss’ Law for magnetism and explain it.

Gauss’s law for magnetism is: The net magnetic flux through any closed surface is zero. The number of magnetic field lines leaving the surface balanced by the number of lines entering it. The net magnetic flux is zero for both the surfaces. This is true for any closed surface.

Consider a small vector area element $∆$S of a close surface S as in figure.
The magnetic flux through $∆$S is defined as ${\mathrm{\Delta \varphi }}_{\mathrm{B}}=\overrightarrow{\mathrm{B}}\cdot \overrightarrow{\mathrm{\Delta S}}$, where B is the field at $∆$S .
We divided S into many small area elements and calculate the individual flux through each.
Then, the net flux $\mathrm{\varphi }$ is
$\mathrm{\varphi }=\sum \overrightarrow{\mathrm{B}}\cdot \overrightarrow{\mathrm{\Delta S}}=$= 0.
where ‘all’ stands for 'all area elements'.
Compare this with Gauss’s law of electrostatics, the flux through a closed surface in that case is given by
$\mathrm{\varphi }=\sum \overrightarrow{\mathrm{E}}\cdot \overrightarrow{\mathrm{\Delta S}}=\frac{\mathrm{q}}{{\mathrm{ϵ}}_0}$
Where q is the electric charge enclosed by the surface.
The difference between the Gauss’s law of magnetism and that for electrostatics is that isolated magnetic poles (also called monopoles) are not known to exist.