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

What is the most important factor in determining climates.

Butane gas reacts with oxygen gas to give carbon dioxide gas and water vapor (gas). if you mix butane and oxygen in the correct stoichiometric ratio, and if the total pressure of the mixture is 390 mmhg, what is the pressure (in mmhg) of water vapor after the reaction is completed (temperature and volume do not change).

What volume of 0.500 mol/l hydrochloric acid, hci (aq) is required to react completely with 1.00 g of aluminum hydroxide, ai(oh)3 (s)?