It is known that wax contracts on solidification. If molten wax is taken in a large vessel and it is allowed to cool slowly, then
A. It will start solidifying from the top downward
B. It will start solidifying from the bottom upward
C. It will start solidifying from the middle, upward and downward at equal rates
D. The whole mass will solidify simultaneously

Hint: Solidification is a phenomenon where the liquid substance will be converted into the solid. Like water converting into ice when temperature is decreased, the same happens in case of wax too. But it is slightly different from the water solidification due to the different internal properties of wax.

Complete step-by-step answer:
Before discussing the solidification we should discuss the phase changes. Generally matter exists in three states like solid, liquid and gaseous phase. When solids are heated they are converted to liquids and when liquids are heated they are converted to gases. The process of conversion of solid to liquid due to heating is called melting and the process of conversion of liquid to gas is called evaporation. These are the phase change mechanisms and during these phase changes temperature will remain the same.
The process of conversion of liquid to solid is called solidification.
The way in which wax is different from ice is, during solidification the water will expand. That is the reason why ice has less density than water.
But in case of wax it is completely opposite. Wax contracts during solidification.
When the water is solidified i.e being cooled ice will be starting to form from the top to bottom because of special property of water called anomalous expansion of water i.e water at 4 degree Celsius has the highest density
But wax doesn’t show that property so during solidification wax starts solidifying from bottom to upward.

So, the correct answer is “Option B”.

Note: There is a different effect of pressure on melting point of ice and wax. Generally as the pressure increases for water the melting point will decrease, but in case of wax as the pressure increases the melting point of wax will increase.