Answer:
The correct answer is option b, that is, polyatomic ion.
Step-by-step explanation:
A molecular ion also called polyatomic ion refers to a charged chemical species comprising two or more atoms bonded covalently with each other. The polyatomic ions comprise two or more non-metallic atoms. An example of a polyatomic ion is an ion of nitrate that comprises one atom of nitrogen and three atoms of oxygen. As the atoms in a polyatomic ion are bonded covalently, they are considered to possess a single charged unit.