Calcium nitrate on dissociation gives 2 moles of nitrate ions and one mole of calcium ions, so the total number of moles of ions is 2+1=3.0
It gives three ions hence the Van’t Hoff factor
Van’t Hoff factor
The Van’t Hoff factor offers insight into the effect of solutes on the colligative properties of solutions. It is denoted by the symbol ‘i’. The Van’t Hoff factor can be defined as the ratio of the concentration of particles formed when a substance is dissolved to the concentration of the substance by mass.