Chemical properties of elements are primarily determined by the electrons but not by neutrons. Therefore, the isotopes of the same element have similar chemical behavior. (a) The atomic number is 17, so there are 17 protons and 17 electrons. The mass number is 35, so there are 18 (=35-17) neutrons. Hope this helps. :)
protons and neutrons are in the nucleus electrons surround the atom and i have no idea what positrons are i just know they arent in an atom so your answer is B and C