helium (He) hydrochloric acid (HCl) hydrogen (H2) nitrogen (N2)
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Which chemical is a compound?
Possibilities:
- helium (He)
- hydrochloric acid (HCl)
- hydrogen (H2)
- nitrogen (N2)

hydrochloric acid (HCl)