The cation in MnI3 is Manganese III (Mn3+). This conclusion comes from analyzing the overall charge neutrality of the compound and the valency of iodine.
In MnI3, we have three iodine ions (I–) for every one manganese ion. Since each iodine ion has a -1 charge, the three iodide ions contribute a total of -3 charge. To balance this negative charge, the manganese must have a +3 charge. Therefore, the manganese in MnI3 is in the +3 oxidation state, which is denoted as Manganese III.
Additionally, Manganese can exhibit multiple oxidation states, including +2 and +4, but in the specific case of MnI3, the +3 state is the only one that satisfies the charge balance in the compound.