(1) According to "the number of protons in the nucleus = the number of electrons outside the nucleus = the number of nuclear charges", it can be seen from the diagram of the relationship between the outermost electron number and the number of nuclear charges of the element 1 ~ 18 in the figure that the proton numbers of hydrogen and oxygen are 1 and 8 respectively; Because 1 water molecule consists of 2 hydrogen atoms and 1 oxygen atoms; So a water molecule has three nuclei, 1×2+8= 10 protons;

(2) AM2+is positively charged and loses two electrons, so the number of electrons outside the ion nucleus is:12-2 =10; Cl- is negatively charged with 1 electron, so it is known that the outermost electron number of its ion is 7+ 1=8, so it is the same as Ar and Ne atoms.

(3) By analyzing the diagram, the following laws are summarized: With the increase of nuclear charge, the number of electrons in the outermost layer changes periodically; The number of electron layers of elements in the same period is the same.

So the answer is: (1) 3, 10,10; (2) 10，Ar； (3) With the increase of nuclear charge, the number of electrons in the outermost layer changes periodically; The number of electron layers of elements in the same period is the same.