Arrange the isotopes of sulfur and phosphorus in order of decreasing number of neutrons.
Rank the isotopes from most to fewest neutrons. To rank items as equivalent, overlap them.

S-36
P-35
S-32
P-33
P-32
P-31



Answer :

Neutrons=mass number-atomic number
most          S-36 and P-35(both have 20 neutrons) (36-16=20)(35-15=20)
                 P-33 (33-15=18neutrons)
                 P-32 (32-15=17 neutrons)
least          S-32 and P-31 (both have 16 neutrons) (32-16=16)(31-15=16)