CBSE 2026 · Region 2 · Set 2 · Q25 · 3 marks
(a)$\displaystyle \left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ is paramagnetic whereas $\displaystyle \left[\mathrm{Fe}(\mathrm{CO})_{5}\right]$ is diamagnetic. Justify the statement. [Atomic number of $\displaystyle \mathrm{Fe}=26$ ] $\displaystyle 2+1$(b)On the basis of crystal field theory write the electronic configuration for $\displaystyle \mathrm{d}^{4}$ ion if $\displaystyle \Delta_{0}<\mathrm{P}$.
(a)
$\displaystyle \left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ is paramagnetic whereas $\displaystyle \left[\mathrm{Fe}(\mathrm{CO})_{5}\right]$ is diamagnetic. Justify the statement. [Atomic number of $\displaystyle \mathrm{Fe}=26$ ] $\displaystyle 2+1$
(b)
On the basis of crystal field theory write the electronic configuration for $\displaystyle \mathrm{d}^{4}$ ion if $\displaystyle \Delta_{0}<\mathrm{P}$.
Marking-scheme solution
(a)
In [Fe(H2O)$\displaystyle 6$] $\displaystyle 2$+, H2O is a weak field ligand and 3d electrons do not pair
up. Hence it is paramagnetic.
In [Fe(CO)$\displaystyle 5$] CO is a strong field ligand, pairing takes place. Hence it is
diamagnetic.
(b)
t2g3 eg1
Coordination CompoundsBonding in Coordination CompoundsUnderstandshort_answerhard
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CBSE Class 12 Chemistry past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.