JEE Main · 2024 · 05 Apr 2024 · Shift 1 · Coordination Compounds

Which one of the following complexes will exhibit the least paramagnetic behaviour ?
[Atomic number,

Cr = 24, Mn = 25, Fe = 26, Co = 27

]

(A) $[Co (H_{2} O)_{6}]^{2 +}$ ✓ Correct
(B) $[Fe (H_{2} O)_{6}]^{2 +}$
(C) $[Mn (H_{2} O)_{6}]^{2 +}$
(D) $[Cr (H_{2} O)_{6}]^{2 +}$

Answer: (A)

Solution

Least paramagnetic = fewest unpaired electrons. With weak-field

H_{2} O

(high spin):

C o^{2 +}

^{7}

) has 3 unpaired;

F e^{2 +}

^{6}

) has 4;

M n^{2 +}

^{5}

) has 5;

C r^{2 +}

^{4}

) has 4. The smallest number of unpaired electrons is 3, for

[Co (H_{2} O)_{6}]^{2 +}

, so it shows the least paramagnetic behaviour.

JEE Main · 2024 · 05 Apr 2024 · Shift 1 · Single correct option

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