Step-by-step explanation:
Interstellar clouds is generally is the combination of plasma , ions , gases on our and other galaxies. They contains a lot of ions , molecules and atoms in interstellar.
Radio telescope is the device which detect EM waves of particular frequency in radio waves.
Also the molecules and the chemical compounds presents in interstellar emits waves of radio frequency , so they will be easily detected by radio telescopes.
This is the reason for identification of chemical compounds by radio telescopes.
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