An ice cube that is dropped into a glass of water melts because
a.
the water is liquid, and the ice is solid.
b.
heat energy moves from the ice to the water.
c.
heat energy moves from the water to the ice.
d.
the ice is denser than the water.

C.  heat energy moves from the water to the ice.

Explanation:

When a cold (that is, at a low temperature) and a hot (that is, at a high temperature) bodies are in contact, heat flux from the hot to the cold body. In this case, the ice cube is the cold body and water is the hot one.  

As this happens, the temperature of the ice cube increase and if the heat transferred is high enough, the ice cube change from solid to liquid (melts). At the same time, that water lows its temperature as a consequence of the heat loss.

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).