The IUPAC name of [CoCl(NH_3)_5]Cl_2 is:

The given complex is $[\text{CoCl(NH}_3)_5]\text{Cl}_2$.

The coordination sphere is the cation $[\text{CoCl(NH}_3)_5]^{2+}$ and the counter ion is the chloride anion $\text{Cl}^-$.

Let the oxidation state of cobalt be $x$.

$x + (-1) + 5(0) = +2 \Rightarrow x = +3$

The ligands present in the coordination sphere are ammine ($\text{NH}_3$) and chloro ($\text{Cl}^-$). According to alphabetical order, ammine is written before chloro.

Since there are five ammine ligands and one chloro ligand, the prefix is pentaamminechloro.

The central metal is in a cationic complex, so it is named cobalt, followed by its oxidation state in Roman numerals, which is (III).

The counter ion is named chloride (the number of counter ions is not indicated by prefixes like di or tri).

Combining these parts, the IUPAC name of the complex is pentaamminechlorocobalt(III) chloride.

Answer: Pentaamminechlorocobalt(III) chloride