Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: The spin only magnetic moment value for $[\mathrm{Fe}(\mathrm{CN})_{6}]^{3-}$ is 1.74 BM, whereas for $[\mathrm{Fe}(\mathrm{H}_{2}\mathrm{O})_{6}]^{3+}$ is 5.92 BM. Reason R: In both complexes, Fe is present in +3 oxidation state. In the light of the above statements, choose the correct answer from the options given below:

(A) Both A and R are true but R is NOT the correct explanation of A

(B) $A$ is false but $R$ is true

(D) Both A and R are true and R is the correct explanation of A

JEE Main · 2023 · 06 Apr 2023 · Shift 1 · Coordination Compounds

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: The spin only magnetic moment value for

[Fe (CN)_{6}]^{3 -}

is 1.74 BM, whereas for

[Fe (H_{2} O)_{6}]^{3 +}

is 5.92 BM.
Reason R: In both complexes, Fe is present in +3 oxidation state.
In the light of the above statements, choose the correct answer from the options given below:

(A)Both A and R are true but R is NOT the correct explanation of A✓ Correct
(B) $A$ is false but $R$ is true
(C)A is true but R is false
(D)Both A and R are true and R is the correct explanation of A

Answer: (A)

Solution

In both ions iron is

Fe^{3 +}

, a

d^{5}

system. With the strong-field cyanide ligand the complex

[Fe (CN)_{6}]^{3 -}

is low spin (

t_{2 g}^{5}

), leaving one unpaired electron, so

μ = 1 (1 + 2) = 1.74 BM

. With the weak-field aqua ligand

[Fe (H_{2} O)_{6}]^{3 +}

is high spin with all five electrons unpaired, so

μ = 5 (5 + 2) = 5.92 BM

. Both statements are factually true, and iron is indeed

+ 3

in each, but the moments differ because of ligand field strength, not the oxidation state, so the reason does not explain the assertion. Both A and R are true while R is not the correct explanation of A.

JEE Main · 2023 · 06 Apr 2023 · Shift 1 · Single correct option

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JEE Main · 2023 · 06 Apr 2023 · Shift 1 · Coordination Compounds

Solution

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