By heating sugar is decomposed at approx. 180 oC.
Sugar. You can caramelize sugar on a home stove quite easily. Salt's melting temperature, by contrast, is orders of magnitude higher
Salt will melt first.
Sugar. Salt often slows down the process of melting, so sugar is what would melt it faster.
Salt
sugar
Salt, obviously.
Sugar will melt more easily than salt because sugar has a lower melting point than salt. Sugar will start to melt around 320°F (160°C) while salt requires a higher temperature of around 1474°F (801°C) to melt.
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
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)."