Step 1: Understanding the concept.
Gauss’s law in magnetism states that the net magnetic flux through any closed surface is zero, meaning that there are no isolated magnetic monopoles. This law is one of Maxwell's equations and reflects the fact that magnetic field lines always form closed loops. Step 2: Analyzing the options. (1) Gauss’s theorem in electrostatics: This is incorrect. Gauss's law in electrostatics deals with electric fields, not magnetic fields. (2) Gauss’s theorem in magnetism: Correct. Gauss’s law for magnetism indicates that isolated magnetic monopoles do not exist. (3) Both a and b: This is incorrect. Only Gauss’s law in magnetism explains the absence of magnetic monopoles. (4) None of the above: This is incorrect, as option (2) is correct. Step 3: Conclusion.
The correct answer is (2) Gauss’s theorem in magnetism, as it explains that magnetic monopoles do not exist.