S-36 s-34 p-35 p-32 p-31 p-33
arrange the isotopes of sulfur and phosphorus in order of decreasing number of neutrons.

Decreasing order for number of neutrons: P-35 > S-34= P-33 >S-32= P-31

Explanation:

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons

Phosphorous has atomic number of 15 and thus contains 15 protons and sulphur has atomic number of 16 and thus contains 16 protons.

1. For S-32

Mass number = 32

Atomic number = 16

Number of neutrons = Mass number - Number of protons= 32-16 = 16

2.  For S-34

Mass number = 34

Atomic number = 16

Number of neutrons = Mass number - Number of protons= 34-16 = 18

3. For P-35

Mass number = 35 , Atomic number = 15

Number of neutrons = Mass number - Number of protons= 35-15 = 20

4. For P-31

Mass number = 31

Atomic number = 15

Number of neutrons = Mass number - Number of protons= 31-15 = 16

5. For P-33

Mass number = 33

Atomic number = 15

Number of neutrons = Mass number - Number of protons= 33-15 =18

Decreasing order for number of neutrons: P-35 > S-34= P-33 >S-32= P-31