An oxidation number is a positive or negative number assigned to an element in a chemical compound that represents the hypothetical charge that element would have if all of the bonds in the compound were purely ionic.
The oxidation number of Mn can be determined by looking at its position in the periodic table and the charge of the compound. In most cases, Mn has an oxidation number of +2 or +4, but it can also have other oxidation numbers, such as +6 in permanganate (MnO4-).
Oxidation state and oxidation number are often used interchangeably, but there is a subtle difference between the two. Oxidation state is the charge an atom would have if all the bonds in a compound were purely ionic, while oxidation number is the charge an atom actually has in a compound.
The oxidation number of Mn can vary in different compounds because it has multiple valence electrons, meaning it can form different numbers of bonds with other elements. This results in different oxidation numbers depending on the compound it is found in.
The oxidation number of Mn can affect its reactivity because it determines the number of electrons available for bonding. In compounds where Mn has a higher oxidation number, it is more likely to undergo reduction reactions, while in compounds where it has a lower oxidation number, it is more likely to undergo oxidation reactions.