Question

41. Which one of the following statements concerning 21-cm radiation is false A. It passes freely through the dusk of the Galaxy B. It is composed of very energetic photons C. it is produced when a hydrogen atom's electron changes its spin D. It is seen at radio wavelengths

Can u explain the reason

Answer 1

The answer is b=it is composed of very energetic photons

21-cm radiation is the radio wavelength EM radiation which is emitted by the cold and neutral interstellar hydrogen atoms. So when there is a collision between the particles, atoms may excite and make their spin parallel which results in the a tiny amount of energy generation. As per rules of the quantum mechanics those type of atoms will radiate the obtained energy in the form of the low energy photons corresponding to the 21 cm wavelength.