What is the EAN of Fe in $\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-}$ ?

The Effective Atomic Number (EAN) of Fe in $[\mathrm{Fe}(\mathrm{CN})_6]^{3-}$ is determined using the formula:

$\mathrm{EAN} = Z - \mathrm{OS} + 2 \times \mathrm{CN}$
where $Z$ is the atomic number, $\mathrm{OS}$ is the oxidation state, and $\mathrm{CN}$ is the coordination number.

For iron, $Z = 26$. The oxidation state $x$ satisfies $x + 6 \times (-1) = -3$, yielding $x = +3$. The complex contains six cyanide ligands, so $\mathrm{CN} = 6$.

Substituting these values: $\mathrm{EAN} = 26 - 3 + 2 \times 6 = 35$.

Final answer: $\boxed{35}$