The molecular weight of
NO2=14 (atomic weight of
N )
+2×16 (atomic weight of Oxygen)
The molecular weight of NO2=46g
From Avogadro's rule, 1 mole of the NO2 contains 6.022×1023molecules
⇒ 46g of NO2 contains 6.022×1023molecules
$ 1 g of NO2 contians 6.022×102346g=0.13×1023=0.13×1023molecules
10mg=10×10−3g=0.13×1023×10×10−3=0.13×1021=13×1019molecules
∴ 10mg of NO2 contains 13×1019molecules
Given that 1.8×1019 molecules were removed from 10 mg of NO2
⇒ 13×1019−1.8×1019=(13−1.8)×1019=11.2.×1019molecules
Now we need to convert these molecules to number of moles
If 6.022×1023 molecules is 1 mole (By Avogadro's rule)
11.2×1019 moelcules contians 1 mole6.022×1023mloecules×11.2×1019molecules
=1.87×10−4moles