Question

determine the number of moles 1) 20g Na and 2) 34g H2O

Answer 1

To calculate this, add up the automic mass units of each atom. (That can be found under the element's abbreviation on the periodic table.)
1) Na = 23 amu
 20g / 23 = 0.87 moles Na

2) H = 1.01 O = 16.0 
1.01 + 1.01 + 16 = 18.02
34g/18.02 = 1.89 moles H2O