All of the questions here are pertaining to the colligative properties of a solution and the preparation of solutions. Maybe, it would be best if you understand the equations to be used in order to answer these questions.
Freezing point depression or Boiling point elevation:
ΔT = -K (m) (i)
ΔT is the change in the freezing point or the boiling point not the freezing point/boiling point. Therefore, it should be added to the original value of the property of the solvent.
K is a constant called the molal freezing point depression constant and for the boiling point is the boiling point elevation constant. It is a property of the solvent.
m is the concentration of the solute in the solvent in terms of molality or kg solute/kg solvent.
i is the vant hoff factor which will represent the number of ions which the solute dissociates when in solution.
