Magnetic susceptibility of a diamagnetic substance
A.)Decreases with temperature
B.)Is not affected by temperature
C.)Increases with temperature
D.)First increases then decreases with temperature

Hint: In a diamagnetic substance, the spins are paired and are slightly repelled when placed in a magnetic field. Inter atomic vibrations due to temperature do not affect the pairing of the spins that much.

Detailed step by step solution:
Magnetic materials can be classified into three main categories: Paramagnetic materials, diamagnetic materials and ferromagnetic materials.

Paramagnetic materials are those which are slightly attracted in the direction of the applied magnetic field. Diamagnetic substances are slightly repelled in the external magnetic field. Ferromagnetic substances are strongly attracted in the external magnetic field.

Diamagnetic behaviour of materials arises due to the paired spins of electrons in the material. When such materials are placed in an external magnetic field, they are repelled due to their inner fields.

Magnetic susceptibility is defined as the extent to which a material gets magnetised when placed in an external magnetic field. Diamagnetic materials have negative susceptibility.

When we increase the temperature of a diamagnetic substance, there is not much effect on the susceptibility. The paired spins remain unaffected by the increase in inter-atomic vibrations as a very large amount of energy is required to break apart paired electrons which are in their ground state when paired. So, The susceptibility is basically unaffected with change in temperature for a diamagnetic substance.
So, the most suitable answer is option B.

Note: By Pauli’s exclusion principle, no two electrons can occupy the same state so in order to occupy a state; they pair up with electrons of opposite spin. Also, the magnetic susceptibility of diamagnetic materials will be affected only at a very large temperature.