Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Consider a ferromagnetic material :
Assertion (A) : The individual atoms in a ferromagnetic material possess a magnetic dipole moment and interact with one another in such a way that they spontaneously align themselves forming domains.
Reason (R) : At high enough temperature, the domain structure of ferromagnetic material disintegrates. Thus, magnetization will disappear at high enough temperature known as Curie temperature.
In the light of the above statements, choose the correct answer from the options given below :

Solution

Physics sir · 4 steps

Both lines are textbook facts, but one is about room temperature and the other about heating: no link.

1. Check Assertion. In a ferromagnet each atom carries a magnetic dipole moment. Strong exchange interaction makes neighbouring moments line up on their own, giving small regions called domains. So (A) is true.
2. Check Reason. Heating increases thermal agitation, which breaks up the alignment inside domains. Above the Curie temperature T_C the material turns paramagnetic and loses its spontaneous magnetisation. So (R) is true.
3. Test the link. Ask whether (R) tells us why domains form. It does not: domains form because of the interaction between atomic moments. (R) only says what happens to those domains at high temperature.
4. So. Both statements are true, but (R) is not the correct explanation of (A). The answer is (d).

The idea to keep. In assertion-reason questions, first judge each statement on its own. Then ask whether R answers the 'why' of A. A true fact on the same topic is not automatically the explanation.

Answer from the NTA final answer key. Solution by PrepWiser.