In this question, the sulfur atom has atomic number 16 and atomic mass 33. The Atomic number represents the number of the proton inside the atoms and atomic mass represent the mass of the atoms. Since electron mass to small, the atomic mass can be interpreted as the sum of neutron and proton. Then, the number of the neutron would be:
mass= neutron + proton
33= neutron+16
neutron = 17
