Why do you think egg cells are large and sperm cells are small?

because it gives the sperm a better chance of finding it, and because it makes their numbers large

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.