Why are we giving the answer for a 1st year chemistry test question?

You would merely state the molarity or normality of each different molecule or ion in the solution. The colligative properties of a solution are affected by the sheer number of things that are dissolved in it, however. E.g. things like boiling point elevation and freezing point depression are the physical properties of the solvent that are affected in an additive manner by the amount of added solutes.

If one adds 1 mole of NaCl and 1 mole of CaCl2 to a final adjusted volume of exactly 1 Liter in water, the chloride ion concentration would be additive (1 mole of Cl- from NaCl and 2 moles of Cl- from CaCl2). Thus the solution could be said to be a solution of 1M Na+, 1M Ca+, and 3M Cl-, but normally one would instead merely state that it is a 1M NaCl, 1M CaCl2 solution. So, yes, in some situations, various 'solutes' are indeed additive on a molar basis.

thank you sir