Transition metals are well known for having more than one stable oxidation state. manganese has more than any other.
In its compounds manganese exhibits oxidation states from +2 to +7.
The common oxidation states are +2, +4, and +7, but the less common +3, +5, and +6 states are easily prepared.
Since the colours of the six oxidation states are all different, showing them on an overhead projector makes for a colourful display – alternatively using a visualiser against a white background works well