B. What useful functions do oxidation numbers serve?
20.
b. How many molecules are in 1 mole of
molecules?
c. What is the name given to the number of
molecules in 1 mole?
21. a. What is the molar mass of an element?
b. Write the molar mass rounded to two
decimal places of carbon, neon, iron and
uranium.

Explanation:

b. What useful functions do oxidation numbers  serve?

It is used to show oxidation and reduction (loss and gain of electrons)

b. How many molecules are in 1 mole of  molecules?

1 mole = 6.022 * 10^23 molecules

c. What is the name given to the number of  molecules in 1 mole?

Avogadro's Number of molecules

21. a. What is the molar mass of an element?

This is the mass of an element divided by the number of moles.

Molar mass = Mass / Number of moles

b. Write the molar mass rounded to two  decimal places of carbon, neon, iron and  uranium.

amu = Atomic Mass Unit

Carbon = 12.01 amu

Neon = 20.18 amu

Iron = 55.85 amu

Uranium = 238.03 amu