Question: 71. Given below are two statements;
Statement I: Ferromagnetism is considered as an extreme form of paramagnetism.
Statement II: The number of unpaired electrons in a \mathrm{Cr}^{2+} ion ( \mathrm{Z}=24 ) is the same as that of a \mathrm{Nd}^{3+} ion (\mathrm{Z}=60).
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are true
(2) Both Statement I and Statement II are false
(3) Statement I is true but Statement II is false
(4) Statement I is false but Statement II is true
Answer: Option (3)
Explanation:
Statement I is true. Ferromagnetism arises due to strong alignment of magnetic moments in the same direction,
which is an enhanced or extreme case of paramagnetism caused by strong exchange interactions between unpaired electrons.
Now consider Statement II. The electronic configuration of chromium is [Ar]\,3d^{5}\,4s^{1}. For \mathrm{Cr}^{2+},
two electrons are removed, first from 4s and then from 3d,
giving the configuration [Ar]\,3d^{4}. This results in 4 unpaired electrons.
The electronic configuration of neodymium is [Xe]\,4f^{4}\,6s^{2}.
For \mathrm{Nd}^{3+}, three electrons are removed
(two from 6s and one from 4f), giving [Xe]\,4f^{3}.
This results in 3 unpaired electrons.
Since the number of unpaired electrons in
\mathrm{Cr}^{2+} and \mathrm{Nd}^{3+}
ions is not the same, Statement II is false.
Therefore, the correct answer is Option (3).