Question:

Match the List-I (Phenomenon associated with electromagnetic radiation) with List-II (Part of electromagnetic spectrum) and select the correct code from the choices given below this lists:
List IList II
IDoublet of sodium(A)Visible radiation
IIWavelength corresponding to temperature associated with the isotropic radiation filling all space(B)Microwave
IIIWavelength emitted by atomic hydrogen in interstellar space(C)Short radio wave
IVWavelength of radiation arising from two close energy levels in hydrogen(D)X-rays

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Sodium D lines are yellow (visible); cosmic microwave background peaks in the microwave region; the hydrogen 21 cm line is a radio wave.
Updated On: Nov 11, 2026
  • (I)-(A), (II)-(B), (III)-(B), (IV)-(C)
  • (I)-(A), (II)-(B), (III)-(C), (IV)-(C)
  • (I)-(D), (II)-(C), (III)-(A), (IV)-(B)
  • (I)-(B), (II)-(A), (III)-(D), (IV)-(A)
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The Correct Option is B

Solution and Explanation

I. Sodium doublet (589.0 and 589.6 nm) lies in the visible region: (A).
II. Isotropic radiation filling all space is the cosmic microwave background (about 2.7 K), peaking near 1 mm: microwave (B).
III. Atomic hydrogen in interstellar space emits the 21 cm line: short radio wave (C).
IV. Hyperfine splitting of the hydrogen ground state (two close energy levels) also gives the 21 cm line: radio wave (C).
So I-A, II-B, III-C, IV-C.
Answer: (2) (I)-(A), (II)-(B), (III)-(C), (IV)-(C)
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