what is meant by tetra atomic and poly atomic?
Tetra-atomic may refer to either molecules or ions. Tetra-atomic molecules or ions are those species which are formed when 4 atoms chemically combine together, that is they contain 4 atoms. For example, NH3, SO3 are examples of tetra-atomic molecules, CO32- is a tetra-atomic ion.
For polyatomic molecule, please refer to the following link