Question

On increasing the external pressure, the melting point of wax
$A.$decreases
$B.$increases
$C.$remains unaffected
$D.$none of these

Answer 1

We should use the concept of melting point and its characteristics during change in pressure. Relation between temperature and pressure will be used here. On increasing pressure phase transition temperature also increases.

Complete answer:
We know that with increase in external pressure, the phase transition temperature of the wax also increases. Due to this increase of phase transition temperature the melting point of wax also increases.
Hence, we conclude that on increasing the external pressure, the melting point of wax increases.

Therefore, option $(B)$ is correct.

Additional Information:
We should know some basics of melting point. Melting point of a substance is defined as the fixed temperature at which the substance changes from solid state to liquid state and the process of change of solid state to liquid state is called melting. Melting always occurs at the fixed temperature for a given value of pressure. The melting point of a substance can be changed by changing the pressure also. We should also know that melting is a bulk phenomenon. Melting point of wax is about ${{37}^{o}}C$ or ${{99}^{o}}F$.
We should also know some basics of wax. Wax is a soft and colourless solid. It is derived from petroleum. It is made up of hydrocarbons of about twenty to forty carbon atoms. It is also known as paraffin wax.

Note:
We should remember the fact that the melting point of a substance does change with change in pressure. But at a fixed pressure the melting point is always constant for a given substance. Different materials have different melting points.