The value of $\mathrm{M}-\mathrm{C}$ stretching frequencies of (i) $\left[\mathrm{V}(\mathrm{CO})_{6}\right]^{-}$, (ii) $\left[\mathrm{Cr}(\mathrm{CO})_{6}\right]$ and (iii) $\left[\mathrm{Mn}(\mathrm{CO})_{6}\right]^{+}$following the trend
(a)(ii) > (i) > (iii)
(b)(ii) $>$ (iii) $>$ (i)
(c)(i) > (ii) > (iii)
(d)(iii) $>$ (ii) $>$ (i)
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
More negative charge on the metal increases M→CO back-bonding, strengthening M–C: [V(CO)₆]⁻ > Cr(CO)₆ > [Mn(CO)₆]⁺ — (i) > (ii) > (iii) (c).