Given :
mass of carbon = 5mg =
Atomic mass of carbon=12u
Solution ::
a. The number of moles of carbon in his homework writing
number of moles=
=
= 4.167
b. The number of carbon atoms in 12 mg of his homework writting
mass of carbon =12mg
number of moles =
=
=1 mol
number of atoms of carbon =number of moles avogadros constant
=
= atoms