State Gauss Law of Magnetism.

Gauss Law is only concerned with the total enclosed charge that finally tells us the total flux. The charges outside may change field patterns. They not affect the total flux. It's actually incorrect to assume the field due to the external charges should also affect the flux through the Gaussian surface. 

Gauss Law does not directly give the electric field in all cases. It can only be used in calculations for symmetrical surfaces: spherical, cylindrical, or planar. 

The integral form of Gauss Law is considered as an indirect form and only in theory. It will still create a mathematical problem. The Gaussian surface passing through a discrete charge means it lies on the surface. Half of the electric flux is outside and half in. Not on the boundary. And we know Gauss' Law holds true only when there are closed surfaces. 

According to Gauss’s law magnetism

$?\stackrel{?}{B}.\stackrel{?}{ds}=0$

There are various important topics in the physics chapter 5 class 12 magnetism and matter. These topics are important for both cases, conceptual and numerical questions. Read below:

• Magnetism 
• Bar Magnet as an Electromagnet
• Magnetic Field Due to Magnetic Dipoles
• Type of Magnetic Materials: Ferromagnetic, Paramagnetic, and Diamagnetic
• Magnetisation and Magnetic intensity
• Magnetic Susceptibility
• Magnetic Flux Intensity 
• Potential energy due to a magnetic dipole