The correct option is A Monoatomic
In the case of an element, each molecule is made up of a definite number of atoms. The number of atoms in a molecule of an element is called its atomicity. Monoatomic is when a molecule of an element contains only one atom. For example, Helium - He and Potassium - K. A molecule is diatomic when it contains two atoms. For Example, Nitrogen gas –N2. A molecule is triatomic when it contains three atoms. For Example, Ozone-O3. A molecule is polyatomic when it contains more than three atoms. For Example, Sulphur - S8.