Determine the molecular weight for mg(no3)2. 134.32 g 118.32 g 148.33 g 172.64 g

Molecular Weight (MW) is the sum of the atomic weights/masses (AM) of every atom in a compound or molecule. Thus, we would add the AM of Mg + 2×[N+(O×3)]:
Mg = 24.31
N = 14.01
O = 16
So we have: Mg + 2×[N+(O×3)] = 24.31 + 2×[14.01+(16×3)] = 24.31+2×[14.01+48] = 24.31+ 2×62.01 = 24.31+124.02 = 148.33

C) is the correct answer

Density and pressure