In which of the following complexes the CFSE, $\Delta_{\mathrm{o}}$ will be equal to zero?

In which of the following complexes the CFSE, $\Delta_{\mathrm{o}}$ will be equal to zero?
  1. $\left[\mathrm{Fe}(\mathrm{en})_3\right] \mathrm{Cl}_3$
  2. $\mathrm{K}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]$
  3. $\left[\mathrm{Fe}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Br}_2$
  4. $\mathrm{K}_3\left[\mathrm{Fe}(\mathrm{SCN})_6\right]$

Solution

For complex $\mathrm{K}_3\left[\mathrm{Fe}(\mathrm{SCN})_6\right]$

Calculation of CFSE
$\begin{aligned}
& =(-0.4 \times 3+0.6 \times 2) \Delta_0 \\
& =0 \Delta_0
\end{aligned}$

Asked in: JEE Main 2025 (22 Jan Shift 1)

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