Which of the following is the correct order of the strength of π -acc…

The correct answer is option (1) CN⁻ < RNC < CO < NO⁺.

The strength of a \(\pi \)-acceptor ligand is determined by the electronegativity of the ligand. The more electronegative the ligand, the stronger the pi-acceptor.

In the list of ligands given, CN⁻ is the most electronegative, followed by RNC, CO, and NO⁺. Therefore, the order of pi-acceptor strength is CN⁻ < RNC < CO < NO⁺.

The explanation for the order is as follows:

CN⁻ is the most electronegative ligand because it has a negative charge, which attracts electrons to the ligand.

RNC is less electronegative than CN⁻ because it has a triple bond, which makes the electrons more localized.

CO is less electronegative than RNC because it has a double bond, which makes the electrons more delocalized.

NO⁺ is the least electronegative ligand because it has a positive charge, which pulls electrons away from the ligand.

Therefore, the order of \(\pi \)-acceptor strength is CN⁻ < RNC < CO < NO⁺.