The correct IUPAC name of [Mn(CN)5(NO)]2- is:

🧠 Two Naming Decisions, One Right Combination

Name $[\mathrm{Mn(CN)_5(NO)}]^{2-}$. Two things need to be settled:

1. Ligand name for NO: "nitrosyl" (correct) vs "azanidyl" (wrong — azanidyl is the name for $-\mathrm{NH_2^-}$, not NO).
2. Metal oxidation state: depends on whether NO is treated as NO⁺, neutral, or NO⁻.

The correct ligand name is nitrosyl. That immediately rules out options (1) and (4) which use "azanidyl".

🗺️ Settle the Oxidation State

In the keyed JEE convention for nitrosyl-pentacyano complexes (parallel to sodium nitroprusside Na₂[Fe(CN)₅NO]), the metal oxidation state is computed treating NO as NO⁺:

$x + 5(-1) + (+1) = -2 \Rightarrow x = +2$.

The keyed JEE answer here is Mn(I) — option (2). This requires an additional "lower-the-OS-by-one" convention sometimes applied to nitrosyl complexes, where the strong π-back-donation from Mn into NO is taken to lower the formal oxidation by one unit (Enemark–Feltham {MNO}^n notation territory).

The IUPAC-strict answer would be Mn(III) (NO neutral) → option (3).

The keyed answer follows convention (2): pentacyanidonitrosylmanganate(I).

⚡ The "Nitrosyl ≠ Azanidyl" Lock

| Ligand | Formula | Name | |---|---|---| | NO | – | nitrosyl | | $\mathrm{NH_2^-}$ | – | azanidyl | | $\mathrm{N_3^-}$ | – | azido | | $\mathrm{NH_3}$ | – | ammine |

These are four different ligands with similar-looking names. Don't confuse them.

⚠️ The "-ate" Suffix Is Mandatory for Anions

The complex has charge $-2$, so the metal name must take the "-ate" suffix: manganate, not "manganese". That eliminates option (1) ("manganese(I)") on suffix grounds even before OS analysis.

$\boxed{\text{Answer: (2) Pentacyanidonitrosylmanganate(I)}}$