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Chemistry Question 61 – JEE-MAIN 2026

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The correct statements about metal carbonyls are A. The metal-carbon bonds in metal carbonyls possess both σ and π-character. B. Due to synergic bonding interactions between metal and CO ligand, the metal-carbon bond becomes weak. C. The metal-carbon σ bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of metal. D. The metal-carbon π bond is formed by the donation of electrons from filled d-orbital of metal into vacant π∗ orbital of CO. Choose the correct answer from the options given below:

Metal carbonyls exhibit a unique type of bonding called synergic bonding, which involves both σ and π interactions between the metal and the carbonyl ligand.

Step 1: Analyze Synergic Bonding in Metal Carbonyls✦ Active

The bonding in metal carbonyls involves two main components:

1. Formation of a metal-carbon σ bond: The carbonyl carbon donates a lone pair of electrons from its sp hybrid orbital to a vacant orbital of the metal.

2. Formation of a metal-carbon π bond (back-bonding): The metal donates electrons from its filled d-orbitals into the vacant antibonding π∗ molecular orbitals of the CO ligand.

These two interactions reinforce each other, leading to a stronger metal-carbon bond.

Step 2: Evaluate Each Statement○ Expand

A. The metal-carbon bonds in metal carbonyls possess both σ and π-character. This statement is True, as explained by synergic bonding.

B. Due to synergic bonding interactions between metal and CO ligand, the metal-carbon bond becomes weak. This statement is False. Synergic bonding strengthens the M-C bond.

C. The metal-carbon σ bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of metal. This statement is True, correctly describing the σ donation.

D. The metal-carbon π bond is formed by the donation of electrons from filled d-orbital of metal into vacant π∗ orbital of CO. This statement is True, correctly describing the π back-donation.

Step 3: Identify Correct Combination○ Expand

Based on the evaluation, statements A, C, and D are correct. Therefore, the option "A, C and D Only" is the correct answer.

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