A: In a diamagnetic substance each atom has a non-zero dipole moment but due to thermal agitation the individual dipoles ramein randomly oriented and, therefore, the net dipole moment in any finite volume of the substance remains zero.
R: On increasing the temperature the magnetism inside a perament magent increases.

Options

A. If both Assertion & Reason are the true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reson is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the given assertion and reason problem, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Analyze the Assertion (A)
The assertion states: "In a diamagnetic substance, each atom has a non-zero dipole moment but due to thermal agitation, the individual dipoles remain randomly oriented and, therefore, the net dipole moment in any finite volume of the substance remains zero."

1. **Understanding Diamagnetism**: Diamagnetic substances are characterized by having all their electrons paired. This pairing results in the cancellation of their magnetic moments.
2. **Thermal Agitation**: While thermal agitation does cause random orientations of dipoles, in a diamagnetic substance, the key point is that there are no net dipole moments to begin with because the individual dipoles cancel each other out due to pairing.
3. **Conclusion on Assertion**: Therefore, the assertion is **false** because it incorrectly states that each atom in a diamagnetic substance has a non-zero dipole moment.

### Step 2: Analyze the Reason (R)
The reason states: "On increasing the temperature, the magnetism inside a permanent magnet increases."

1. **Effect of Temperature on Permanent Magnets**: Increasing the temperature typically causes the thermal agitation of the magnetic domains within a permanent magnet.
2. **Impact on Magnetism**: As the temperature increases, the alignment of these magnetic domains becomes disrupted, leading to a decrease in the overall magnetism of the permanent magnet.
3. **Conclusion on Reason**: Thus, the reason is also **false** because increasing the temperature does not increase the magnetism; it actually decreases it.

### Final Conclusion
Since both the assertion and the reason are false, the correct answer is that both A and R are false.

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