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 (Z = 24) is the same as that of a $\mathrm{Nd}{}^{3+}$ ion (Z = 60). In the light of the above statements, choose the correct answer from the options given below:

Solution & Explanation

\textbf{Answer:} (a) Statement I is true but Statement II is false \textbf{Solution:} Statement I is correct: in ferromagnetic substances the unpaired-electron spins of neighbouring atoms align in the same direction, giving a very strong magnetisation. This is regarded as an extreme (cooperative) form of paramagnetism. Statement II is wrong. $\mathrm{Cr}{}^{2+}$ is $3\mathrm{d}{}^4$, which has 4 unpaired electrons. $\mathrm{Nd}{}^{3+}$ is $[\mathrm{Xe}]4\mathrm{f}{}^3$, which has only 3 unpaired electrons. The counts (4 vs 3) are not the same. Hence Statement I is true but Statement II is false.