1. Identify the complex ion and counter ions

The compound is $[Co(NO_2)(NH_3)_5]Cl_2$

So, the coordination entity is: $[Co(NO_2)(NH_3)_5]^{2+}$ with two $Cl^-$ ions as counter ions.

2. Find the oxidation state of cobalt

Let the oxidation state of Co be $x$.

• $NH_3$ is a neutral ligand, so contribution = $0$
• $NO_2^-$ has charge $-1$
• Overall charge on the complex ion = $+2$

Therefore, $x + (-1) + 5(0) = +2$ $x - 1 = 2$ $x = +3$

So cobalt is in the $+3$ oxidation state.

3. Name the ligands

• $NH_3$ is named ammine
• $NO_2^-$ can coordinate through N or O. Here it is written as $NO_2$, and in nomenclature, when bonded through nitrogen, it is named nitrito-N.

Since there are five ammine ligands, we write: $\text{pentaammine}$

4. Order of ligands in naming

Ligands are named in alphabetical order, ignoring multiplicative prefixes.

• ammine
• nitrito-N

Alphabetically, ammine comes before nitrito-N.

Hence ligand part is: $\text{pentaammine nitrito-N}$

5. Name the metal with oxidation state

The complex ion is cationic, so the metal name remains cobalt. Thus: $\text{cobalt(III)}$

6. Add the counter ion name

The outside ion is $Cl^-$, so it is named chloride.

7. Final IUPAC name

Therefore, the full name is: $\boxed{\text{pentaammine nitrito-N-cobalt(III) chloride}}$

8. Check options

• A: nitrito-N-pentaamminecobalt (III) chloride ❌ ligand order wrong
• B: nitrito-N-pentaamminecobalt (II) chloride ❌ wrong oxidation state and ligand order
• C: pentaammine nitrito-N-cobalt (II) chloride ❌ wrong oxidation state
• D: pentaammine nitrito-N-cobalt (III) chloride ✅ correct

So the correct option is D.