Question

If an iron (III) complex with the formula $\left[ \text{Fe}(\text{NH}_3)_x (\text{CN})_y \right]^-$has no electron in its $e_g$ orbital, then the value of $x + y$ is:

• A. 5
• B. 6
• C. 3
• D. 4

Answer 1

Answer: (B)

6

Answer 2

The given complex is
$[\text{Fe}(\text{NH}_3)_2(\text{CN})_4]^{3+}$
Here, the oxidation state of iron is $+3$, which corresponds to a $d^5$ electronic configuration in the high-spin state. The ligands cyanide ($\text{CN}^-$) and ammonia ($\text{NH}_3$) are arranged such that the $e_g$ orbitals remain unoccupied.
Given values:
$x = 2 \, (number\ of \text{NH}_3 \, \text{ligands})$,
$y = 4 \, (\text{number of } \text{CN}^- \, \text{ligands})$
Thus, $x + y = 2 + 4 = 6$.