Molar mass of a molecule is the sum of the atomic mass of the individual elements in the molecule.
Atomic mass of Pb = 207 amu
Atomic mass of N = 14 amu
Atomic mass of O = 16 amu
Here amu stands for atomic mass unit
Molar mass of Pb(NO₃)₂ = 207 + [14 + (16 x 3)] x 2
= 207 + 28 + (48) x 2 = 331 g/mol
