A 50g cube of ice and 500g of boiling water are mixed in an open container. Which of the following is most likely to occur? 

Compared to the phase transition from water to steam, the phase change from ice to water takes less thermal energy. In nature, a process that uses less energy to complete will do so more quickly. This is practically clear given that obtaining the energy to initiate a process or reaction is its primary necessity. It will occur more quickly if less energy is needed.
The moment the ice cube is placed in the boiling water, it begins to absorb heat from the environment (the boiling water). The ice cube melts extremely quickly because boiling water produces such intense heat. Starting and maintaining the phase transition from ice to water needs a lot less energy than

In nature, a process that uses less energy to complete will do so more quickly. This is practically clear given that obtaining the energy to initiate a process or reaction is its primary necessity. It will occur more quickly if less energy is needed.
As a result, the ice cube quickly and readily absorbs all of the heat energy during the phase transition from ice to water. At the same time, the water in the container stops boiling, allowing the ice cube to melt more spontaneously.

Hence, the correct answer is option C.