How can we know that atoms exist and understand them if they are invisible?

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.

Which of the following units is not an official si unit

How many moles of oxygen gas are produced from the decomposition of six moles of potassium chlorate