Answer: C.) polyatomic anion
Step-by-step explanation: Cations are the ions which carry a positive charge and anions are the ions which carry a negative charge. Monoatomic ions are those which consists atoms of similar elements and polyatomic ions are those which consists of atoms of different elements.
For example :
is a monoatomic cation.
is an monoatomic anion.
is a polyatomic cation.
is a polyatomic anion as it consists of atoms of phosphorous and oxygen and bears a negative charge.