Question

Which one of the following has the lowest melting point?
A. $N$
B. $P$
C. $As$
D. $Sb$

Answer 1

Hint : In order to answer the question, to know the lowest melting point, as we should know that the element that is present in solid form at room temperature has the highest melting point and those that are in gaseous form have the lowest melting point.

Complete Step By Step Answer:
In option (A), Nitrogen exists as ${N_2}$ in gaseous form at room temperature. Their small size results in weak Van Der Waals interaction, resulting in low boiling point and melting point.
Melting point of Nitrogen is $- 209.9^\circ C$ .
In option (B), Melting point of Phosphorus is $44.1^\circ C$ . Note that these points are associated with the standard atmospheric pressure. In general, melting is a phase change of a substance from the solid to the liquid phase.
In option(C), Melting point of Arsenic is ${\mathbf{817}}^\circ {\mathbf{C}}$ . In general, melting is a phase change of a substance from the solid to the liquid phase.
In option (D), Melting point of Antimony is $630.63{\text{ }}^\circ C$ .
Now, as we can see that, Nitrogen has the lowest melting point as it is in the form of gas at room temperature, whereas the other optional elements are present in solid at room temperature.
Hence, the correct option is (A).

Note :
The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as $1{\text{ }}atmosphere{\text{ }}or{\text{ }}100{\text{ }}kPa$ .