The atomic number of an element is determined by the number of protons present in its nucleus. In the case of chlorine, it has 17 protons. This means that the atomic number of chlorine is 17. Therefore, the correct answer is B) 17.
In the context of the atomic structure, the neutrons do not affect the atomic number but do contribute to the atomic mass. Electrons, while equal in number to protons in a neutral atom, do not play a role in determining the atomic number either. Thus, regardless of how many neutrons or electrons are present, the atomic number remains based solely on the proton count.