What does hydrochloride mean?

As changes in energy levels of electrons increase, the frequencies of atomic line spectra they emit

Harry lives in a city, and he has a lung condition known as asthma. on certain days, harry has to stay inside because pollutants in the air make it difficult for him to breathe. which of these pollution sources are nonpoint sources that might bother harry if he goes outside? choose the two that apply.

How is the way a mixture is combined different from how a compound is combined?