What is the IUPAC name of K₄[Fe(CN)₆]?

Potassium hexacyanoferrate (II)

The correct answer is option 2. Potassium hexacyanoferrate (II).

To understand the naming of \( \text{K}_4[\text{Fe}(\text{CN})_6] \) according to IUPAC nomenclature, let us break it down step-by-step:

Identify the cation and the anion:

The cation is \( \text{K}^+ \) (potassium).

The anion is \([\text{Fe}(\text{CN})_6]^{4-}\) (a complex ion).

Name the complex ion \([\text{Fe}(\text{CN})_6]^{4-}\):

The ligands are cyanide ions (CN\(^-\)). In the name, the prefix "hexa-" indicates that there are six cyanide ligands. The central metal is iron (Fe). In the name, it is represented as "ferrate" because the complex ion is negatively charged. To determine the oxidation state of the iron, consider the charges:

Cyanide (CN\(^-\)) has a charge of -1 each.

There are six cyanide ligands, contributing a total charge of -6.

The overall charge of the complex ion is -4.

Let the oxidation state of iron be \( x \). Then, the sum of the charges is: \( x + 6(-1) = -4 \), which simplifies to \( x - 6 = -4 \), so \( x = +2 \).

Therefore, the oxidation state of iron is +2.

Combine the names:

The complex ion \([\text{Fe}(\text{CN})_6]^{4-}\) is named "hexacyanoferrate(II)", where "(II)" indicates the oxidation state of iron. The cation potassium (K\(^+\)) is named as "potassium".

Combine the names of the cation and the anion to form the full compound name:

The complete name is "Potassium hexacyanoferrate(II)". Therefore, the correct IUPAC name for \( \text{K}_4[\text{Fe}(\text{CN})_6] \) is Potassium hexacyanoferrate (II).