The $\mathrm{Mo}-\mathrm{Mo}$ bond order in $\left[\left(\eta^{5}-\mathrm{C}_{5} \mathrm{H}_{5}\right) \mathrm{Mo}(\mathrm{CO})_{2}\right]_{2}$ which obeys the 18-electron rule is ____
Answer
Answer (as printed): 3
The options are missing from the source scan for this question, so there is nothing here for this letter to point at. The letter is what the book printed.
Explanation
Answer: 3 — CpMo(CO)₂ is a 15-electron fragment (Mo 6 + Cp 5 + 2 CO 4), so each Mo needs 3 more electrons from the metal–metal bond: a Mo≡Mo triple bond.