$6-8$ A sample is found to contain $0\mathrm{.}800$ mole of a chemical

substance.

a$.$ How many atoms are present if the substance is the

element $Al?$

b$.$ How many atoms are present if the substance is the

elemen$$ Ca$?$

c$.$ How many molecules are present if the substance is

the compound $N{O}_2?$

d$.$ How many molecules are present if the substance is

the compound $N{F}_3?$