Assertion: The ferromagnetic substance do not obey Curie's law.
Reason: At Curie point a ferromagnetic substance start behaving as a paramagnetic substance.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
• If Assertion is true but Reason is false.
• If Assertion is false but Reason is true.

The assertion and reason provided relate to the behavior of ferromagnetic substances in relation to Curie's law and the Curie point. Let's break down each statement:

Assertion Analysis

The assertion states that ferromagnetic substances do not obey Curie's law. This is false because Curie's law applies to paramagnetic materials, while ferromagnetic materials exhibit a more complex behavior that includes a temperature-dependent magnetization that does not strictly follow Curie's law.

Reason Evaluation

The reason given is that at the Curie point, a ferromagnetic substance starts behaving as a paramagnetic substance. This statement is true because at the Curie point, ferromagnetic materials lose their magnetic properties and transition to a paramagnetic state.

Conclusion

Based on the evaluations:

• The assertion is false.
• The reason is true.

Therefore, the correct answer is: If Assertion is false but Reason is true.