What molecules can be found in the interstellar medium? a. water, carbon dioxide, and hydrogen. b. oxygen, nitrogen and ammonia. c. nitrogen, carbon dioxide and oxygen. d. hydrogen, helium and methane.

The interstellar medium is the matter as well as the radiations that are found in the galaxies occupying the spaces between the star systems.
Interstellar medium is mainly composed of hydrogen that is followed by helium and trace amounts of nitrogen, oxygen and carbon (considered traces when compared to amount of hydrogen).

Therefor, the right choice is:
A. Water, Carbon dioxide, and Hydrogen

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