Why does pond water freeze easier than salt water?
Saltwater has a much lower freezing point (the freezing point is the temperature where something freezes) than fresh water does. The more salt there is in water, the lower is the freezing point.
Fresh water freezes at a higher temperature than salty water does. That is because the dissolved salt has a chemical bond with the water in which it is dissolved, and in order for water molecules to bond with each other in the freezing process, they first must break the bond that they have with the dissolved salt.
It depends on how you're trying to freeze them, of course: if you have a freezer that goes to 0 degrees F, like the one in the back room of a supermarket, it'll take as long to freeze the salt water as it would plain water. (Salt water has a lower freezing temperature than plain water but if you have a cold-enough freezer, it'll freeze.) If you pour it into liquid nitrogen, it'll freeze instantly…