$\mathrm{Conc}. {\mathrm{H}}_2{\mathrm{SO}}_4$ displaces hydrogen chloride from chlorides because

First off, let's be clear that the substance being discussed is sulfuric acid. Numerous physical and chemical characteristics exist in it, such as the compound's colorlessness. Now that we are aware of the composition, it is simple to choose the right response, which is that the chemical is a strong acid.

To answer the question, we must determine the proper acid formula. The acid's physical characteristics must then be understood since they will determine the procedure that it will carry out. After learning about the qualities, we may utilise them to determine which of these choices is the best one.

We must first discuss the physical makeup of sulfuric acid. It is a potent mineral acid that has no colour when it is pure. This substance is also one that is employed as a chemical intermediary. It is employed in the production of other compounds and the cleaning of metal surfaces.
Therefore, for the relevant question, we should bear in mind a variety of statistics and information.

$\mathrm{Conc}. {\mathrm{H}}_2{\mathrm{SO}}_4$ displaces hydrogen chloride from chlorides because it is considered stronger acids.

Gas ( $\mathrm{HCl}$, more volatile) can be displaced more easily from the chloride salt solution by ${\mathrm{H}}_2{\mathrm{SO}}_4$​ which is less volatile. 

$\mathrm{NaCl}+\underset{\mathrm{Less} \mathrm{volatile}}{{\mathrm{H}}_2{\mathrm{SO}}_4\to }{\mathrm{NaHSO}}_4+\underset{\mathrm{More} \mathrm{volatile}}{\mathrm{HCl}}$

Therefore the correct answer is $\mathrm{HCl}$ is a gas while ${\mathrm{H}}_2{\mathrm{SO}}_4$ is a liquid.​
Hence, option D is correct.