Deliquescent Compound:
Deliquescent compounds are substances that have a strong affinity for moisture from the air and can absorb enough water to dissolve and form a solution. This property makes them very useful as drying agents or desiccants.

ZnCl2:
- Zinc chloride (ZnCl2) is a deliquescent compound.
- When exposed to air, it absorbs moisture and forms a solution by dissolving in the water it absorbs.
- This property is due to the high solubility of zinc chloride in water and its ability to attract and hold onto water molecules from the surrounding environment.
- The deliquescent nature of zinc chloride makes it useful in various applications where moisture needs to be removed from a system or environment.

Other Compounds:
- HgCl2 (Mercury(II) chloride), Hg2Cl2 (Mercury(I) chloride), and CdCl2 (Cadmium chloride) are not deliquescent compounds.
- These compounds do not have the same strong affinity for moisture as zinc chloride, and they do not readily absorb water from the air to form solutions.
- While they may still react with water or moisture in certain conditions, they do not exhibit the same deliquescent properties as zinc chloride.
In conclusion, among the given options, ZnCl2 is the deliquescent compound due to its ability to absorb moisture from the air and form a solution.