QJEEM21Che8c3: JEE Main 2021 Chemistry - Class 12 JEEM21Che8c3 Solution: Which one of the following species doesn't have a magnetic…

Species does not have a magnetic moment of 1.7 BM means species must not contain single unpaired electron.

(a) Molecular orbital configuration of O $_2^ +$ (15 electrons) is

${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\sigma _{2p_z^2}}\,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,\pi _{2p_x^1}^ * \, = \,\pi _{2p_y^o}^ *$

Unpaired electron = 1

$\mu = \sqrt {n(n + 2)} = \sqrt {1(1 + 2)} = \sqrt 3 = 1.73$

where n = no. of unpaired e ^$-$

$\therefore$ $\mu$ = 1.73 BM

(b) Cul $\Rightarrow$ Cu⁺ $-$ [Ar]3d¹⁰, Unpaired electron = 0

I ^$-$ $\to$ [Xe], unpaired electron = 0

Therefore, $\mu$ = 0

(c) [Cu(NH₃)₄]Cl₂

Cu²⁺ $\to$ [Ar]3d⁹

Unpaired electron = 1,

Therefore, $\mu$ = 1.73 BM

(d) Molecular orbital configuration of $O_2^ -$ (17 electrons) is

${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\sigma _{2p_z^2}}\,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,\pi _{2p_x^2}^ * \, = \,\pi _{2p_y^1}^ *$

Unpaired electron = 1

Therefore, $\mu$ = 1.73 BM

Therefore, Cul does not have magnetic moment of 1.73 BM.