Determine the percentage composition of each of the following compounds

Question

a) NaCl
b) AgNO3
c) Mg(OH)2

for NaCl i got na=23/135=0.17 x 100= 17% Cl=35/135=0.26 x 100=26%

for AgNO3 i got 108/42 which im sure was wrong and i didn't get how to complete the problem..
for Mg(OH)2 i didn't have a clue

Answer 1

In a), where did the 135 come from?
In b), where did the 42 come from?

See my answer to your previous post of the same question.