You can't determine the chemical formula of a compound with just the number of chlorine atoms. You need more information! Here's why:

* Many compounds can contain three chlorine atoms. For example:

* Chlorine trifluoride (ClF₃)

* Trichloromethane (CHCl₃), also known as chloroform

* Phosphorus trichloride (PCl₃)

* Aluminum trichloride (AlCl₃)

* The other elements in the compound matter. To know the exact formula, you need to know the other elements present and their quantities.

For example:

If you know that the compound contains three chlorine atoms and one phosphorus atom, then the formula would be PCl₃ (phosphorus trichloride).

Let me know if you have more information about the compound, and I can help you determine the formula!