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

The Correct Option is B

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, \(x + y = 2 + 4 = 6\).