Question

Arrange the isotopes of sulfur and phosphorus in order of decreasing number of neutrons.

Answer 1

I do not believe you're asking this...
OK. Sulfur has a total of 24 isotopes. Every isotope has 16 protons and the number of neutrons ranges from 10 to 33 inclusive.
Phosphorus has a total of 23 isotopes. They have 15 protons, and between 9 and 31 neutrons inclusive. So here we go.

S-49
S-48
S-47, P-46
S-46, P-45
S-45, P-44
S-44, P-43
S-43, P-42
S-42, P-41
S-41, P-40
S-40, P-39
S-39, P-38
S-38, P-37
S-37, P-36
S-36, P-35
S-35, P-34
S-34, P-33
S-33, P-32
S-32, P-31
S-31, P-30
S-30, P-29
S-29, P-28
S-28, P-27
S-27, P-26
S-26, P-25
P-24

If you're looking for STABLE isotopes, then the list is much smaller.
S-36
S-34
S-33
S-32, P-31

Answer 2

Answer:

Rank of the isotopes from most to fewest neutrons:

S-36, P-35

P-33

P-32

S-32, P-31

Explanation:

The following options are missing:

S-36

P-35

S-32

P-33

P-32

P-31

Sulfur has 16 protons then S-36  has 36 - 16 = 20 neutrons and S-32 has 32 - 16 = 16 neutrons.

Phosphorus has 15 protons, then  P-35 has 35 - 15 = 20 neutrons,  P-33 has 33 - 15 = 18 neutrons,  P-32 has 32 - 15 = 17 neutrons and P-31 has 31 - 15 = 16 neutrons.