Carbon's mass number =12
Hydrogen's mass number=1
( 10×12)+(8×1)
=128
128g =1mol
------- -------
1.98g ?
1.98
------=0.015
128
1mol =6.0×10^23
------ --------------
0.015mol ?
0.015mol×6.0×10^23= 9×10^21
Thus the number of particles in 1.89 grams of napthalene is 9×10^21.
I sincerely hope this is correct.
