Number of complexes which will exhibit synergic bonding amongst, [Cr(CO)6],[Mn(CO)5]CrCO6,MnCO5 and [Mn2(CO)10]Mn2CO10 is

Synergic bonding, also known as back bonding, is a type of chemical bonding where there is a donation of electrons from a metal to a ligand and then back-donation from the ligand to the metal. This type of bonding is commonly observed in metal carbonyl complexes.

1. [Cr(CO)6]: This complex will exhibit synergic bonding. The chromium metal has vacant d-orbitals that can accept electrons from the carbon monoxide ligands. The carbon monoxide ligands can then accept electrons back from the chromium metal, forming a synergic bond.

2. [Mn(CO)5]: This complex will also exhibit synergic bonding. The manganese metal has vacant d-orbitals that can accept electrons from the carbon monoxide ligands. The carbon monoxide ligands can then accept electrons back from the manganese metal, forming a synergic bond.

3. CrCO6: This is not a valid chemical formula, so it cannot exhibit synergic bonding.

4. MnCO5: This is also not a valid chemical formula, so it cannot exhibit synergic bonding.

5. [Mn2(CO)10]: This complex will exhibit synergic bonding. The two manganese metals each have vacant d-orbitals that can accept electrons from the carbon monoxide ligands. The carbon monoxide ligands can then accept electrons back from the manganese metals, forming a synergic bond.

So, the number of complexes which will exhibit synergic bonding amongst the given complexes is 3.