* HCl exists in different forms:

* Hydrogen chloride (HCl) gas: This is the pure form of the compound, and its density will depend on the temperature and pressure.

* Hydrochloric acid (HCl(aq)) is a solution of HCl gas dissolved in water. The density of this solution varies greatly depending on the concentration of HCl.

* Aqueous solutions: Density changes with the concentration of HCl (percentage of HCl in the solution).

To find the density of HCl, you need to specify:

* Are you interested in the density of the gas, or a solution?

* If it's a solution, what is the concentration of HCl?

For example:

* The density of pure hydrogen chloride gas (HCl) at standard temperature and pressure (STP) is about 1.64 g/L.

* A concentrated hydrochloric acid solution (37% HCl by weight) has a density of approximately 1.19 g/mL at room temperature.

Always remember to check the context and information provided to determine the specific density of HCl you need.