The wavelength 21 cm emitted by atomic hydrogen in interstellar space

1.	The wavelength 21 cm emitted by atomic hydrogen in interstellar space belongs to
A.	Radio waves
B.	Infrared waves
C.	\[m=M\]
D.	g-rays
Answer» B. Infrared waves

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The wavelength 21 cm emitted by atomic hydrogen in interstellar space belongs to

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