The correct IUPAC name of [CoCl2(en)2]Cl is: (en = ethane-1,2-diamine)

🧠 Two Hidden Tests

This question hides two IUPAC traps inside one cation:

1. Bis vs di: ethane-1,2-diamine has a numerical prefix (1,2-diamine) inside its name → must use bis(...), not "di-".
2. Modern ligand stems: it's "chlorido" (post-2005), not "chloro" (pre-2005).

Either trap alone kills two of the four options.

🗺️ Construct the Name

Ligands and order.

• "chlorido" comes before "ethane-1,2-diamine" alphabetically.
• 2 × chlorido → "dichlorido" (simple stem → di-).
• 2 × en → "bis(ethane-1,2-diamine)" (composite → bis-).

Oxidation state. Inside bracket: $x + 2(-1) + 2(0) = +1 \Rightarrow x = +3$. So Co(III).

Counter-ion. Outer $\mathrm{Cl^-}$ → "chloride".

Stitched: Dichloridobis(ethane-1,2-diamine)cobalt(III) chloride — option (1).

⚡ The Two-Filter Sweep

For any en-containing complex, run two filters:

• "Ethylenediamine" or "ethane-1,2-diamine"? Modern IUPAC uses ethane-1,2-diamine.
• "Dichloro" or "dichlorido"? Modern IUPAC uses chlorido.

Both filters together usually leave one survivor.

⚠️ The "Bis" vs "Di" Drift

Option (4) writes "dichlorobis(ethane-1,2-diamine)" — correctly uses bis but uses the old "chloro" stem. Mixing modern and old conventions in one name is the most common JEE trap on this style of question.

$\boxed{\text{Answer: (1) Dichloridobis(ethane-1,2-diamine)cobalt(III) chloride}}$