When is the oxidation state of a metal indicated in the name of a compound?
a. when the charge on the nonmetal is not known
b. when the metal can exist in more than one oxidation state
c. when the compound being named is a covalent compound
d. when a prefix is used to indicate the number of metal atoms

B

Explanation:

The oxidation state is present in metals that have multiple oxidation states. Most transition metals have multiple oxidation states. Such as, Iron(II) and Iron (III).

When the metal can exist in more than one oxidation state

Explanation:

When metal exhibit more than one oxidation sate, we have to write the oxidation number of the metal in front of it to for a better clarity.

Most of the transition metals exhibit more than one oxidation state due to presence of d electrons.

For example  the oxidation state of iron are "+2 and +3"

The oxidation state of copper are "+1 and +2"

The oxidation state of Mn are :"+2", +4, +7.

so we generally write there oxidation state in roman

For Mn compound in +2 oxidation state we write Mn(II)

For Mn compound in +7 oxidation state we write Mn(VII)