How many oxygen atoms are in 1.90 g of quartz?

The chemical formula for quartz is SiO₂. It has a molar mass of 60.08 g/mol. We use this to find the moles of quartz.

Moles of quartz = 1.90 g (1 mol/60.08 g) = 0.03162 moles

From the chemical formula, there are 2 moles of Oxygen per 1 mole of SiO₂.

Moles of oxygen = 0.03162 moles*2 = 0.063249 moles O

We use the Avogadro's number, 6.022*10²³ atoms/mole, to find the number of oxygen atoms.

0.063249 moles O * 6.022*10²³ atoms/mole = 3.81*10²² atoms of oxygen