Salt will melt first.
Sugar. Salt often slows down the process of melting, so sugar is what would melt it faster.
Yes. You could try melting it over a Bunsen burner - the sugar will melt readily whereas the salt will not. You could also try dissolving the substance in alcohol. The salt will dissolve only very slightly, but the sugar will dissolve readily.
Salt
sugar
== == Salt lowers the freezing point of water by 32 degrees. If salt is sprinkled onto ice, it causes the ice to melt by a heat transfer. Out of the substances listed, salt would melt ice most efficiently.
Salt, obviously.
You need to determine what you think will melt the fastest, and that will be your hypothesis. If you think that pepper will melt it faster, you would say "My hypothesis is that the pepper will melt ice faster than the other variables (sand, salt, and sugar)."
Sugar. You can caramelize sugar on a home stove quite easily. Salt's melting temperature, by contrast, is orders of magnitude higher
Sugar melts faster than salt because sugar has a lower melting point than salt. Sugar typically begins to melt at around 320°F (160°C), whereas salt does not fully melt until it reaches temperatures exceeding 1,472°F (800°C).
Salt
Salt
No, because you can't boil sugar. It will decompose beforehand. However, you can distinguish sugar and salt by heating them. Sugar will melt and decompose before 300 Celsius. Salt will not melt until ~800 Celsius