MCQ
Which of the following complex compounds will exhibit highest paramagnetic behaviour ?
(At. No. $Ti = 22, Cr = 24, Co = 27, Zn = 30$)
- A$[Ti(NH_3)_6]^{3+}$
- ✓$[Cr(NH_3)_6]^{3+}$
- C$[Co(NH_3)_6]^{3+}$
- D$[Zn(NH_3)_6]^{2+}$
✓
Answer
Correct option: B.
$[Cr(NH_3)_6]^{3+}$
b
$\mathrm{Ti} \rightarrow[\mathrm{Ar}] 3 d^{2} 4 s^{2}, \mathrm{Ti}^{3+} \rightarrow[\mathrm{Ar}] 3 d^{1} 4 s^{0}$ $(1$ unpaired electron)
$\mathrm{Ti} \rightarrow[\mathrm{Ar}] 3 d^{2} 4 s^{2}, \mathrm{Ti}^{3+} \rightarrow[\mathrm{Ar}] 3 d^{1} 4 s^{0}$ $(1$ unpaired electron)
$\mathrm{Cr} \rightarrow[\mathrm{Ar}] 3 d^{4} 4 s^{2}, \mathrm{Cr}^{3+} \rightarrow[\mathrm{Ar}] 3 d^{3} 4 s^{0}$ $(3$ unpaired electrons)
$\mathrm{Co} \rightarrow[\mathrm{Ar}] 3 d^{7} 4 s^{2}, \mathrm{Co}^{3+} \rightarrow[\mathrm{Ar}] 3 d^{6} 4 s^{0}$ $(0 \text { unpaired electrons because of pairing })$
$\mathrm{Zn} \rightarrow[\mathrm{Ar}] 3 d^{10} 4 s^{2}, \mathrm{Zn}^{2+} \rightarrow[\mathrm{Ar}] 3 d^{10}$ (no unpaired electrons)
$\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ exhibits highest paramagnetic behaviour as it contains $3$ unpaired electrons.
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