Given below are two statements :
Statement - I : Susceptibilities of paramagnetic and ferromagnetic substances increase with decrease in temperature.
Statement - II : Diamagnetism is a result of orbital motions of electrons developing magnetic moments opposite to the applied magnetic field.
Choose the correct answer from the options given below

Statement I: Susceptibilities of paramagnetic and ferromagnetic substances increase with decrease in temperature.

For paramagnetic materials, Curie's law states $$\chi = \frac{C}{T}$$, so susceptibility increases as temperature decreases. This is true.

For ferromagnetic materials, below the Curie temperature, the susceptibility increases significantly as temperature decreases (the material becomes more strongly magnetized). Above the Curie temperature, it follows the Curie-Weiss law $$\chi = \frac{C}{T - T_c}$$, which also increases as temperature decreases toward $$T_c$$. So Statement I is true.

Statement II: Diamagnetism is a result of orbital motions of electrons developing magnetic moments opposite to the applied magnetic field.

This is true. Diamagnetism arises because the applied magnetic field modifies the orbital motion of electrons, inducing a net magnetic moment that opposes the applied field (Lenz's law at the atomic level). This effect is present in all materials but is very weak.

Since both statements are true:

Hence, the correct answer is Option A.