The nucleus of an isotope of chlorine contains 20 neutrons

true

Explanation:

i say this because an atom of chlorine-35 contains 18 neutrons (17 protons + 18 neutrons = 35 particles in the nucleus) while an atom of chlorine-37 contains 20 neutrons (17 protons + 20 neutrons = 37 particles in the nucleus). Adding or removing a neutron from an atom's nucleus creates isotopes of a particular element.

i think so it’s will be b yes i believe its

nuclear fission produces elements that are heavier than helium.

the elements that are used in nuclear fission and their products are much heavier than helium.