How many grams is 2.5 x 10^22 molecules of CH4?

0.67 grams of CH4

Explanation:

To convert from molecules to grams, you need to first convert to moles then convert to grams.

Avogadro's Number (6.022 x 10^23) tells us how many molecules are in a mole.

(2.5 x 10^22) / (6.022 x 10^23) = 0.041514 moles of CH4

Then we convert from moles to grams by multiplying moles of CH4 by the molar mass.

0.041514 moles of CH4 x 16.04 g = 0.67 grams of CH4