When $[\text{Cr}(\text{NH}_3)_6]\text{Cl}_3$ dissolves in water, the three chloride ions present outside the coordination sphere ionise completely:

This yields $1$ complex cation $[\text{Cr}(\text{NH}_3)_6]^{3+}$ and $3$ chloride anions $\text{Cl}^-$, giving a total of $1 + 3 = 4$ ions.

In $[\text{Co}(\text{en})_3]_2(\text{SO}_4)_3$:

• Ethane-1,2-diamine ($\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2$, abbreviated as en) is a neutral bidentate ligand (charge $= 0$).
• Sulphate ion ($\text{SO}_4^{2-}$) has a charge of $-2$.

Let the oxidation state of cobalt be $x$:

$[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$ is a square planar complex of the type $\text{MA}_2\text{B}_2$. It displays geometrical (cis-trans) isomerism:

• Cis-isomer (cisplatin): The two identical chloride ligands (and the two ammine ligands) occupy adjacent positions (at an angle of $90^\circ$). Cisplatin is an effective anti-cancer drug.
• Trans-isomer: The two chloride ligands occupy opposite positions (at an angle of $180^\circ$).
  Because it does not contain ambidentate ligands (no linkage isomerism), has no counter ions (no ionisation isomerism), and has only one coordination sphere (no coordination isomerism), it specifically exhibits geometrical isomerism.

IUPAC naming of $[\text{Co}(\text{NH}_3)_5\text{Cl}]\text{Cl}_2$:

• In the coordination entity, ligands are named in alphabetical order: 'ammine' precedes 'chlorido' $\rightarrow$ pentaamminechlorido.
• The coordination sphere is cationic ($[\text{Co}(\text{NH}_3)_5\text{Cl}]^{2+}$), so the central metal retains its regular English name 'cobalt' (not cobaltate).
• Oxidation state of cobalt: $x + 5(0) + (-1) = +2 \implies x = +3$, written in Roman numerals as (III).
• The ionizable anion is named as 'chloride' (the numerical prefix 'di-' is never used for counter ions).