Heating a permanent magnet causes vibration of magnetic dipoles, so their alignment in one particular direction is lesser so loss of magnetic behaviour.

Due to Excessive heat atoms move more rapidly, and started disturbing the magnetic domains. As the atoms are speed up, the percentage of magnetic domains spinning in the same direction is decreases. This lack of cohesion weakens the magnetic force and eventually demagnetizes it entirely.

In contrast, when a magnet is exposed to extreme cold, the atoms slow down so the magnetic domains are aligned and in turn it becomes, strengthened.

Magnetic permeability has SI unit Henry per meter that can also be represented as newtons per ampere square. Hence, option D is correct

Relative magnetic permeability is defined as the ratio of permeability of medium to the permeability of free space.

Magnetic susceptibility is defined as the ratio of the intensity of magnetization M to the magnetizing field intensity H.

For a linear magnetic material subjected to the action of a magnetizing field intensity H and develops magnetization M and induction B, we can write

Where μ₀ is the permeability of free space.

We know that

Comparing

As  , so

Hence D is the correct option.

When diamagnetic material is placed in an external magnetic field, the spin motion of which produce the magnetic moments in the direction of external field slow down while the electrons which produce magnetic moments in opposite direction get accelerated.
Thus, a net magnetic moment is induced in the opposite direction of the applied magnetic field. Hence, the substance is magnetized opposite to the external field.