salt
yes
Sand abosorbs light better then ice. So the heat melts the ice.
Sand doesn't melt ice to any noticeable degree. However, sand picks up heat from sunlight better than pure ice, which can speed up melting a little bit.
It depends on the temperature of the sand and the ice! Sand does not dissolve in water to any significant extent, so that mixing sand with ice will not lower the melting point of the ice. If there is a sufficient amount of sand and it has a temperature above the freezing point of water, sand will eventually melt ice by heat conduction from the sand to the ice. If the sand has a lower temperature than the ice, mixing them will never produce melting of the ice.
No, only the mass of the ice and the temperature of its enviorment matters how fast it will melt. Also, both the amount of direct and indirect heat does make a difference to how fast it will melt.
Salt
it all depends on the temperature. ice melts faster at higher temperatures
Cold water will not melt the ice cube in record time, but hot water will, but salt water will also melt it fast, but if you add both together the ice cube will melt alot fast. Deceasing time alot.
boiling water
because it does!
Salt