Analyze Statement I

Ferromagnetic substances have spontaneous magnetization due to alignment of atomic magnetic moments in domains.

This property strongly depends on temperature:

• At low temperature, exchange interaction keeps magnetic moments aligned.
• As temperature increases, thermal agitation opposes this alignment.
• Above a certain temperature called the Curie temperature $T_C$, the ferromagnetic order is destroyed.

Hence, above the Curie temperature, a ferromagnetic substance behaves as a paramagnetic substance.

Therefore, Statement I is true.

Analyze Statement II

A ferromagnetic specimen consists of domains separated by domain walls.

With increase in temperature, thermal agitation tends to disturb ordered alignment of domains. Near and above the Curie temperature, the ferromagnetic domain structure disappears because long-range ferromagnetic ordering is lost.

So it is not correct to say that at high temperature the domain wall area increases as a general property. Rather, ferromagnetism itself vanishes and the domain structure ceases to exist above the Curie temperature.

Therefore, Statement II is false.

Choose the correct option

• Statement I: True
• Statement II: False

So the correct option is: $\boxed{\text{B}}$

Comparison with stored answer

Stored correct answer: B

My derived answer: B

Hence, my answer agrees with the stored answer.