Question

To melt the ice on your driveway, you can use two moles of rock salt (NaCl) or two moles of calcium chloride (CaCl2). Which solute will have the greatest effect and why?
a) NaCl because it is completely soluble in water.
b) NaCl because it produces fewer moles of solute particles per mole of compound.
c) CaCl2 because it produces more moles of solute particles per mole of compound.
d) CaCl2 because it is less volatile than NaCl.

Answer 1

$CaCl_2$ because it produces more moles of solute particles per mole of compound.

Explanation:

Freezing point depression depend on the "amount of solute particles" . Freezing point is also a colligative property. As we know, calcium chloride  will dissociate into 3 particles  whereas sodium chloride dissociate into only 2 particles. So, an aqueous solution calcium chloride would be effective than sodium chloride.  

Also the water's boiling point with calcium chloride is higher. So $CaCl_2$ is considered as a good  road salt since it produces more ions per formula unit of  salt that is  dissolved  than NaCl  

Answer 2

I know it would be calcium chloride, not sure why. Maybe someone could answer that part.