Which would have the greatest effect on the freezing point of water the addition of sugar or the addition of salt ?

Salt
Water will normally freeze at 0 °C. However, seawater does not freeze at 0 °C, as the presence of salt lowers its freezing temperature to below 0 °C. 

Salt makes ice melt faster because there are more molecules in salt then there are in sugar

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.