The number of bridging CO ligand(s) and Co–Co bond(s) in Co₂(CO)₈, respectively are:

🧠 Structure of $\mathrm{Co_2(CO)_8}$ in the Solid State

In its solid-state form, $\mathrm{Co_2(CO)_8}$ has:

• 2 bridging CO ligands (μ-CO).
• 6 terminal CO ligands (3 on each Co).
• 1 Co–Co bond connecting the two metal centres.

🗺️ Geometry Around Each Co

Each Co is bonded to:

• 3 terminal CO,
• 2 bridging CO (shared with the other Co),
• 1 Co–Co bond.

That's 6 connections → distorted octahedral around each Co. Total: 8 CO ligands (2 bridging + 6 terminal) and 1 metal–metal bond.

⚡ 18-Electron Count Sanity Check

Co(0) d⁹. Each terminal CO contributes 2 electrons; each bridging CO contributes 1 electron (per metal); Co–Co bond contributes 1 electron.

Per Co: $9 + 3(2)_{\text{terminal}} + 2(1)_{\text{bridging}} + 1_{\text{M-M}} = 9 + 6 + 2 + 1 = 18$ ✓.

The 18-electron rule is satisfied — consistent with stability of $\mathrm{Co_2(CO)_8}$.

⚠️ Solid State vs Solution

In solution, $\mathrm{Co_2(CO)_8}$ exists in equilibrium between the bridged (solid-state) form and a non-bridged form (all 8 CO terminal, with Co–Co bond). JEE typically asks about the solid-state structure.

$\boxed{\text{Answer: (1) 2 and 1}}$