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

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If assertion and reason both are false.

Explanation

To solve the question regarding the assertion and reason about ferromagnetic substances and Curie's law, we can break it down into a step-by-step analysis:

### Step 1: Understand the Assertion
The assertion states that "ferromagnetic substances do not obey Curie's law."

- **Curie's Law** states that the magnetic susceptibility (χ) of paramagnetic materials is inversely proportional to the temperature (T). This means that as temperature increases, the susceptibility decreases.
- **Ferromagnetic materials**, however, behave differently at temperatures below a certain point known as the Curie point (Tc). Below this temperature, they exhibit strong magnetism, while above it, they behave like paramagnetic materials.

### Step 2: Analyze the Reason
The reason states that "at the Curie point, a ferromagnetic substance starts behaving as a paramagnetic substance."

- This statement is true. At the Curie point, ferromagnetic materials lose their ferromagnetic properties and transition to a paramagnetic state.

### Step 3: Evaluate the Truth of the Assertion and Reason
- The assertion is **incorrect** because ferromagnetic substances do obey Curie's law, but only after they transition to a paramagnetic state at the Curie point.
- The reason is **correct** because it accurately describes the behavior of ferromagnetic substances at the Curie point.

### Step 4: Conclusion
Based on the analysis:
- The assertion is false.
- The reason is true.

Thus, the correct conclusion is that the assertion is incorrect while the reason is correct.

### Final Answer
The assertion is false, and the reason is true.

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