I need help I don't understand how you are supposed to do this

Asingle atom of an element has 21 neutrons, 20 electrons, and 20 protons. which element is it? ok o z

If you need to add 27.50ml of a solution, which piece of glassware would you use to deliver this volume and explain how you would determine if the 27.50 ml was measured?

If 2 molecules of one reactant combine with 3 molecules of another to produce 5 molecules of a product, then what is the representation of the reaction?