How many protons do all chlorine atoms have?
Every chlorine atom has 17 protons, 17 fundametal positively charged nuclear particles.
Elemental identity is defined by the number of protons, fundamental, massive, positively charged nuclear particles. The number of protons give
Do you have to remember these numbers? NO, because for every test in Chemistry and Physics you will ever sit, you should be supplied with a Periodic Table of Elements as a matter of course. You still have to be able to use the Table, so get on the case.