Question

Moles of Zn(NO3)2 in 131.50g of this substance.

Answer 1

number of moles= mass / molecular masss
mass 131.50g
molecular mass of Zn(NO3)2 =189.39 g/mol
number of moles = 131.50 g/189.39 g/mol =0.69433 mol

Answer 2

molecular mass of Zn(NO3)2 = molecular mass of Zn + two times (molecular mass of N + 3 times molecular mass of O)
molecular mass of Zn(NO3)2 = 65.38 + 2 x (14 + 3 x 15.99)