explain whether sodium chloride or calcium chloride would be a more effective substance to melt the ice on a slick sidewalk.

Answer 1

The colligative property equation is
delta T = i*Kf*m
where i is the van't Hoff factor. It is the number of particles.
NaCl ionizes to two particles.
CaCl2 ionizes to three particles.
So which will have the greater effect, everything else being the same.