What is the oxidation state of iron in the complex ${\text{K}}_4[\text{Fe}(\text{CN}{)}_6]$?

Solution

1. The complex is ${\text{K}}_4[\text{Fe}(\text{CN}{)}_6]$.
2. Let the oxidation state of iron be $x$.
3. The charge balance equation is $4(+1) + x + 6(-1) = 0$.
4. Solving for $x$, we get $4 + x - 6 = 0$, which implies $x=+2$.
5. Hence the answer is (A).