Q5 / 160 · AP EAMCET 2021 (25 Aug Shift 1) · Chemistry

Which of the following element, has the highest number of unpaired electrons in it's ground state?

  • A
    $\mathrm{Mn}$
  • Correct answer
    B
    $\mathrm{Cr}$
  • C
    $\mathrm{Ni}$
  • D
    $\mathrm{Fe}$

Solution

The electronic configurations of the given elements are as $$ \begin{aligned} & { }_{25} \mathrm{Mn}=[\mathrm{Ar}] 3 d^5 4 s^2 \quad(\therefore 5 \text { unpaired electrons }) \\ & { }_{24} \mathrm{Cr}=[\mathrm{Ar}] 3 d^5 4 s^1 \quad(\therefore 6 \text { unpaired electrons }) \\ & { }_{28} \mathrm{Ni}=[\mathrm{Ar}] 3 d^8 4 s^2 \quad(\therefore 2 \text { unpaired electrons }) \\ & { }_{26} \mathrm{Fe}=[\mathrm{Ar}] 3 d^6 4 s^2 \quad(\therefore 4 \text { unpaired electrons }) \\ & \end{aligned} $$ Hence, ${ }_{24} \mathrm{Cr}$ is having highest number of unpaired electrons i.e., 6 $$ \text { Magnetic moment }=\sqrt{6(6+2)}=\sqrt{48}=6.92 \mathrm{BM} $$ (Highest magnetic moment)

Hence, the correct answer is option: 'B'.

Relevant Questions