formula for quartz =SiO(subscript 2)
Quartz has molecular mass of 60.09 g/mol. 1.80 g quartz multiplied by 1 mol quarts/60.09g gives .0300 mol quartz. In each mole of quartz, there are two moles of oxygen (from sio-2-). That gives .0600 mol oxygen. There are approx. 6.02×10^23 atoms in a mole.
.0600 mol oxygen times 6.02×10^23 atoms/mol gives 3.61×10^22 atoms of oxygen.