JEE Chemistry 2026 Question with Solution

Given: Two statements about paramagnetic species and the order of number of unpaired electrons in iron complexes.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

Step 1: Analysis of Statement I

is high spin and paramagnetic.

contains one unpaired electron and is paramagnetic.

contains unpaired electrons and is paramagnetic.

is low spin due to strong field ligand $\mathrm{CN^-}$ and has unpaired electrons.

Hence, $3$ species are paramagnetic. Statement I is true.

Step 2: Analysis of Statement II

$\mathrm{CN^-}$ is a strong field ligand causing pairing of electrons, while $\mathrm{H_2O}$ is a weak field ligand causing maximum unpaired electrons.

Thus, the given increasing order of unpaired electrons is correct:

Statement II is true.

Conclusion: Both Statement I and Statement II are correct. The correct option is D.

Given: Strong field ligands like $\mathrm{CN^-}$ cause electron pairing, while weak field ligands like $\mathrm{H_2O}$ increase paramagnetism.

Find: Whether each statement is true using ligand strength and unpaired electron count.

For Statement I, the solution states that:

• $[\mathrm{CoF_6}]^{3-}$ is high spin and paramagnetic.
• $[\mathrm{TiF_6}]^{3-}$ has one unpaired electron and is paramagnetic.
• $\mathrm{V_2O_5}$ is paramagnetic.
• $[\mathrm{Fe(CN)_6}]^{3-}$ is low spin but still has unpaired electrons.

Therefore, the count of paramagnetic species is taken as $3$, so Statement I is true.

For Statement II, the solution uses ligand field strength:

• $\mathrm{K_4[Fe(CN)_6]}$ has the fewest unpaired electrons because $\mathrm{CN^-}$ is a strong field ligand.
• $\mathrm{K_3[Fe(CN)_6]}$ has more unpaired electrons than $\mathrm{K_4[Fe(CN)_6]}$.
• $\mathrm{[Fe(H_2O)_6]SO_4 \cdot H_2O}$ has more unpaired electrons because $\mathrm{H_2O}$ is a weak field ligand.
• $\mathrm{[Fe(H_2O)_6]Cl_3}$ has the maximum unpaired electrons in this sequence.

So the increasing order is correct, and Statement II is true.

Conclusion: Both statements are true, so the correct option is D.