(a) We know that, 1 mole of carbon atoms = Gram atomic mass of carbon = 12 g

Also, 1 mole of carbon atoms = 6.022 x 10^23 atoms of carbon.

Therefore

6.022 x 10^23 atoms of carbon weigh = 12 g

So, 1 atom of carbon weigh

(b) We know that,

1 mole of sodium atoms = Gram atomic mass of sodium = 23 g

Mass of 0.02 mole of sodium = 0.02 x 23 g = 0.46 g

© 1 mole of H20 = Gram molecular mass of H20 = 1x2 +16 = 18 g

We know that, 1 mole of H2O

= 1 mole = 6.022 x 10^23 molecules

It means that, 6.022 x 10^23 molecules of water have mass = 18 g

Therefore

1 molecule of H20 have mass 18 g