MHT CET Chemistry Question (2026) — Solution

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The oxidation state of Co in [ Co(NH _3)_6]^ 3+ is +3. The electronic configuration of Co is [ Ar ] 3d^7 4s^2. The electronic configuration of Co^ 3+ is [ Ar ] 3d^6. Since NH _3 acts as a strong field ligand for Co^ 3+ , pairing of electrons takes place in the 3d subshell. All 6 electrons pair up in the inner d-orbitals, leaving two 3d orbitals empty. The number of unpaired electrons is 0. The complex undergoes d^2sp^3 hybridization, resulting in an octahedral geometry. Answer: 0, octahedral