M = n / V
Where, M is molarity (M or mol/L), n is number of moles of the solute (mol) and V is volume of the solution (L).
Here the solute is KNO₃.
The given molarity is 1.3 M
This means 1L of solution has 1.3 moles of KNO₃.
Hence moles in 600 mL = 1.3 M x 0.6 L = 0.78 mol
Therefore to make 1.3 M KNO₃ solution, needed moles of KNO₃ is 0.78 mol
