Assertion: [Co(en)3]3+ is paramagnetic. Reason: [Co(en)3]3+ is an inn…

The correct answer is option 4. Assertion is wrong statement but reason is correct statement.

Let us break down the explanation step-by-step to clarify why the assertion and reason lead to the conclusion that the assertion is incorrect but the reason is correct.

Assertion: \([Co(en)_3]^{3+}\) is paramagnetic

In the complex \([Co(en)_3]^{3+}\), the cobalt ion is in the +3 oxidation state. Cobalt's atomic number is 27, so its ground state electronic configuration is \([Ar] 3d^7 4s^2\). When cobalt loses three electrons to form \(\text{Co}^{3+}\), its electronic configuration becomes \([Ar] 3d^6\).

Ethylenediamine (en) is a bidentate ligand and a strong field ligand. Strong field ligands cause pairing of electrons in the d-orbitals.

In an octahedral crystal field, the \(3d\) orbitals split into two sets: \(t_{2g}\) (lower energy) and \(e_g\) (higher energy). For a \(d^6\) configuration in the presence of strong field ligands like en, the electrons pair up in the \(t_{2g}\) orbitals:

\((t_{2g})^6 (e_g)^0 \)

This means all six 3d electrons occupy the three \(t_{2g}\) orbitals, and all are paired.

Paramagnetism arises from unpaired electrons. Since \([Co(en)_3]^{3+}\) has no unpaired electrons (all are paired), it is diamagnetic, not paramagnetic.

So, the assertion is incorrect because \([Co(en)_3]^{3+}\) is actually diamagnetic (no unpaired electrons).

Reason: \([Co(en)_3]^{3+}\) is an inner orbital complex

Inner orbital complexes use the inner d orbitals for hybridization. In an octahedral field with strong field ligands, \(\text{Co}^{3+}\) \((d^6)\) undergoes \(d^2sp^3\) hybridization, using the 3d, 4s, and 4p orbitals. This means the complex uses the inner \((n-1)d\) orbitals (in this case, 3d orbitals). An inner orbital complex has d orbitals from the penultimate shell involved in bonding.

For \(\text{Co}^{3+}\), the 3d orbitals are the inner \((n-1)d\) orbitals, making \([Co(en)_3]^{3+}\) an inner orbital complex.

So, the reason is correct because \([Co(en)_3]^{3+}\) uses the 3d orbitals for hybridization, which are the inner orbitals.

Therefore, the correct evaluation is: Assertion is wrong statement but reason is correct statement.