How many of each kind of atom is in one molecule of water

There are two hydrogen atoms and one oxygen atom aka H2O.

In a molecule, the number after the element symbol indicates the number of atoms of that element in the molecule. The chemical formula for water is H2O. The two after the H (hydrogen) which stands for hydrogen, indicates that there are two hydrogen atoms in the molecule. Since there are no numbers after the O (Oxygen), that means there is only a single atom of that element.

So, there are two hydrogen atoms and one oxygen atom in one molecule of water.

Hope this helps! :)

4, two dominant and two recessive