How many oxygen atoms are in 2.80 g of quartz?

The chemical formula for quartz is SiO₂

Percentage by mass of oxygen = (2 x 16) x 100 / (28 + 2 x 16)

Percentage by mass of oxygen = 53.3%

Mass of oxygen in sample = 0.533 x 2.8

Mass of oxygen = 1.49 grams

Moles of oxygen = 1.49 / 16

Moles = 0.093

One mole contains 6.02 x 10²³ particles

Thus, the atoms of oxygen:

0.093 x 6.02 x 10²³

= 5.6 x 10²²