I forget... how do you find the proton, neutron and electron in an element?

Answer 1

By looking inside.

or

I think you are asking how does one know how many of each are in an atom of a particular element.

It this case by looking at the periodic table an element like oxygen O is number 8. That means it has 8 electrons, and 8 protons and since its atomic weight is lightly over 16 it also has 8 neutrons. (Neutrons weigh just a teensy-weensy more that protons.)

Have fun

Answer 2

Well its a bit easy

The atomic number will give you the number of protons. Ok that's good. The number of electrons (negative) always equal the number of protons (positive) because they have to balance. Then if you subtract the atomic weight from the atomic number you should have the number of neutrons (ignore the small decimal difference, its because of other trace isotopes).

Have fun, check that periodic table it should all be there