How many moles of water can be made from 4 moles of oxygen gas and 16 moles of hydrogen gas?

Both oxygen and hydrogen under normal conditions contain two atoms per mole. 4 moles of oxygen therefore contain 8 moles of oxygen atoms, which is sufficient to make 8 moles of water, since water contains only one oxygen atom per molecule. The 16 moles of hydrogen contain 32 moles of hydrogen atoms. Only 16 moles of hydrogen atoms are needed to make 8 moles of water, which contains 2 hydrogen atoms per mole. Therefore, oxygen is the limiting constituent in this mixture, and 8 moles of water can be made from the specified amounts.