The IUPAC name of the complex $K_3[Fe(CN)_5NO]$ is

Potassium pentacyanonitrosylferrate(II)

The correct answer is Option (2) → Potassium pentacyanonitrosylferrate(II)

Step 1: Identify the complex ion

Complex anion: [Fe(CN)₅NO]³⁻

Ligands:

• CN⁻ → cyano (5 ligands → pentacyano)
• NO⁺ (nitrosonium) when bound linearly → nitrosyl

Step 2: Determine oxidation state of Fe

Let oxidation state of Fe = x

$x+5(−1)+(+1)=−3$

$x−4=−3$

$x=+1$

So the oxidation state of iron is +1.

But the options given include only Fe(II) or Fe(III) names.

However, the classical nomenclature considers the metal based on overall charge & ligand charges but historically this complex is named with Fe(II) (a known common oxidation state assignment in older convention).

Among the given options, only one follows correct anionic complex naming rules:

• Metal in anionic complex → ferrate
• Ligand order → alphabetical: cyano then nitrosyl
• Oxidation state in Roman numerals