Since the given is in grams, convert it first to moles.
Molecular weight of NaCN (the solute):
Na = 11
C = 12
N = 14
TOTAL = 37 grams
1.9 x 10^-4 g. NaCN x 1 mole = 0.00005135135
37 grams
Given:
Mole of solute: 0.00005135135 mol
Liter of solution: 100 ml/1000 = 0.1 L.
Molarity = moles of solute
liter of solution
= 0.00005135135
0.1 L
= 0.0005135135 mol/L. or 5.1 x 10^-4 mol/L.