Correct IUPAC name \([Co(NH_3)_5Cl]Cl_2\) is:

Pentaamminechloridecobalt(III)chloride

The correct answer is option 2. Pentaamminechloridecobalt(III)chloride.

To determine the correct IUPAC name for the complex \([Co(NH_3)_5Cl]Cl_2\), let's break down the complex and follow the IUPAC naming conventions:

Central Metal Ion: Cobalt (Co)

Ligands: 5 ammonia molecules \((NH_3)\), which are neutral ligands, 1 chloride ion \((Cl^-)\) as a ligand.

Counter Ions: 2 chloride ions \((Cl^-)\) outside the coordination sphere.

Oxidation State of Cobalt:

The complex ion is neutral, and the charges must balance.

Ammonia \((NH_3)\) is neutral, so the oxidation state of cobalt is determined by the chloride ion within the coordination sphere \((Cl^-)\).

Let the oxidation state of cobalt be \(x\):

\(x + 0 \times 5 + (-1) = +1 \text{ (charge of the complex ion)}\)

\(x - 1 = +1 \implies x = +3\)

Therefore, cobalt is in the \(+3\) oxidation state.

IUPAC Naming Conventions:

Ligands are named first in alphabetical order, followed by the metal ion. Prefixes like "penta-" indicate the number of ligands (e.g., "pentaammine" for five ammonia ligands). The oxidation state of the metal is indicated in Roman numerals in parentheses. The name of the anion ligand (chloride) comes after the ammonia ligands. The name of the counter ion(s) (outside the square brackets) is placed at the end.

Applying These Conventions:

Ligands:

"Ammonia" is named "ammine."

"Chloride" is named "chloride."

Metal: Cobalt in the \(+3\) oxidation state is named "cobalt(III).

Counter Ions: The two chloride ions outside the coordination sphere are named "chloride."

The correct IUPAC name is Pentaamminechloridocobalt(III) chloride.