What is the gram molecular mass of a compound if 5 moles of the compound has a mass of 100 grams?

The gram molecular mass of a compound whose 5 moles has a mass of 100 grams would be 20 grams per mole.

The gram molecular mass of a substance is simply the mass (in gram) of 1 mole of the same substance. In other words, the gram molecular mass of a substance is also the same as the molar mass of the substance.

In this case, 5 moles of the substance weigh 100 grams

Therefore, 1 mole of the same substance would weigh:

                     1 x 100/5 = 20 grams

More on the gram molecular mass can be found here: link

1 gram molecular mass of this compound = 20

Explanation:

Gram Molecular Mass is the mass of a chemical that is obtained by the number of grams in the chemical determined by the masses obtained from the periodic table and the number of mols determined from the Chemical formula.

That's quite a mouthful. Here's what it means in plain language.

Find the Gram molecular mass of C2H6

The periodic table tells us that 1 mol of C2H6 has

2 mols of Carbon which is 2*C or 2 * 12 = 24 and

6 mols of Hydrogen which is 6*H or 6*1 =  6

The gram molecular mass is 6 + 24 = 30

Your question doesn't require all that background.

5 gram molecular masses = 100 grams       Given

1 gram molecular mass   = x

5/1 = 100/x          Cross multiply

5x = 100             Divide by 5

x = 100 / 5

x = 20