How many grams of SnO2 are required to produce 1.20x10^21 molecules of water?

Explanation:

The balanced chemical reaction to obtain water from SnO₂ is:

The mole ratio is:

Find the number of moles equivalent to  1.20× 10²¹ molecules of water, using Avogadro's number:

From the mole ratio, the number of moles of SnO₂ are half the number of moles of water. That is:

Use the molar mass of SnO₂ to convert the number of moles to grams:

The answer must be reported with 3 significant figures.