Answer:
1.244x10^23 molecules
Explanation:
From Avogadro's hypothesis, 1mole of any substance contains 6.02x10^23 molecules.
This means that 1mole of SiO2 contains 6.02x10^23 molecules
1mole of SiO2 = 28 + (2x16) =28 +32 = 60g
If 1 mole(i.e 60) of SiO2 contains 6.02x10^23 molecules,
Therefore, 12.40g of SiO2 will contain = (12.40 x 6.02x10^23) / 60 = 1.244x10^23 molecules
