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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3cc057

Take $H X_{2} O$ and $F X^{-}$ as weak field (high spin) and $CN X^{-}$ as strong field (low spin). Select the correct comparisons.

ASpin-only moment: $[Fe (H X_{2} O) X_{6}] X^{2 +}$ is greater than $[Mn (CN) X_{6}] X^{4 -}$
BMagnitude of CFSE (pairing ignored) is greater for $[Fe (CN) X_{6}] X^{4 -}$ than for $[Fe (H X_{2} O) X_{6}] X^{2 +}$
C $[Ni (H X_{2} O) X_{6}] X^{2 +}$ and $[NiCl X_{4}] X^{2 -}$ (tetrahedral) have the same number of unpaired electrons
DWith the same $Δ_{o}$ and $Δ_{t} = \frac{4}{9} Δ_{o}$ , the magnitude of CFSE of tetrahedral $[CoCl X_{4}] X^{2 -}$ is greater than that of octahedral $[Co (H X_{2} O) X_{6}] X^{2 +}$

Answer: A, B, C

Fe(II) high spin has 4 unpaired (

4.90

BM) and Mn(II) low-spin

d^{5}

has 1 (

1.73

BM), so the first is true. CFSEs are

2.4 Δ_{o}

and

0.4 Δ_{o}

, so the second is true. Ni(II)

d^{8}

has 2 unpaired in both. For Co(II)

d^{7}

: octahedral

0.8 Δ_{o}

and tetrahedral

1.2 Δ_{t} = 0.533 Δ_{o}

, so the last is false.

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