Q41 / 180 · COMEDK 2019 · Chemistry
Which one of the following shows highest magnetic moment?
- Correct answerA$\mathrm{Fe}^{2+}$
- B$\mathrm{Co}^{2 t}$
- C$\mathrm{Cr}^{3+}$
- D$\mathrm{Ni}^{2+}$
Solution
Atomic number of $\mathrm{Fe}(26)=[\mathrm{Ar}] 3 d^{6} 4 s^{2}$
$$
\mathrm{Fe}^{2+}=[\mathrm{Ar}] 3 d^{6} 4 s^{0}
$$
Number of unpaired electrons $=4$ For Co ${ }^{2+}=[\mathrm{Ar}] 3 d^{7}$ Number of unpaired electrons $=3$ It shows highest magnetic moment. As magnetic moment depends on number of unpaired electrons. For Cr ${ }^{3+}=[\mathrm{Ar}] 3 d^{3}$ $\therefore$ Number of unpaired electrons $=3$ For $\mathrm{Ni}^{+}=[\mathrm{Ar}] 3 d^{8}$ $\therefore$ Number of unpaired electrons $=2$
Number of unpaired electrons $=4$ For Co ${ }^{2+}=[\mathrm{Ar}] 3 d^{7}$ Number of unpaired electrons $=3$ It shows highest magnetic moment. As magnetic moment depends on number of unpaired electrons. For Cr ${ }^{3+}=[\mathrm{Ar}] 3 d^{3}$ $\therefore$ Number of unpaired electrons $=3$ For $\mathrm{Ni}^{+}=[\mathrm{Ar}] 3 d^{8}$ $\therefore$ Number of unpaired electrons $=2$
Hence, the correct answer is option: 'A'.