What is the mass of 40.34x10^23 H2 molecules ar STP​

In a closed or isolated system , matter can not be created or destroyed. it can change forms but is conserved true or false

Which statements describe polyatomic ions? check all that apply. polyatomic ions have many charges. polyatomic ions have one overall charge. polyatomic ions repel other ions to form ionic bonds. polyatomic ions attract other ions to form ionic bonds. polyatomic ions are made up of only one type of atom. polyatomic ions are made up of two or more types of atoms.

__can be defined as which velocity changes