Assertion: [Co(en)₃]³⁺ is paramagnetic. 
Reason: [Co(en)₃]³⁺ is an inner orbital complex.

Assertion is wrong statement but reason is correct statement.

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.