If 3.011 x 1023 molecules have a mass of 20.04 grams, what is the molar mass of this substance?

The molar mass is the mass of one mole of substace.

So, the molar mass is calculate by the formula:

molar mass = mass in grams / number of moles

Then, first you have to calculate the number of moles, using Avogadro's number:

number of moles = 3.011 * 10^ 23 / 6.022 * 10 ^ 23 = 0.5 moles

=> molar mass = 20.04 grams / 0.5 moles = 40.08 g / mol

Answer: 40.08 g / mol