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(D) At room temperature,hydrogen atoms are in the ground state $(n=1)$.When ultraviolet light passes through the gas,photons with energies correspondi

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All of the above.

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(D) At room temperature,hydrogen atoms are in the ground state $(n=1)$.When ultraviolet light passes through the gas,photons with energies corresponding to transitions from $n=1$ to higher energy levels $(n=2, 3, 4, ...)$ are absorbed by the hydrogen atoms. Consequently,these specific wavelengths are missing from the beam $A$ emerging in the $x-$ direction.When the excited electrons return to lower energy levels,they emit photons. These emitted photons emerge in the $y-$ direction as beam $B$.Since the absorbed wavelengths correspond to the energy difference between $n=1$ and higher states,the emitted photons in $B$ will have wavelengths corresponding to transitions from higher states to lower states (e.g.,$n=2$ to $n=1$,$n=3$ to $n=2$,etc.).Thus,the wavelengths absent in $A$ are exactly those that are re-emitted in $B$.Furthermore,transitions to $n=3$ or higher levels (e.g.,$n=4$ to $n=3$) result in the emission of infrared light. Therefore,$B$ will contain some infrared light.

List-$I$	List-$II$
$1$. Nitrogen molecules	$(A)$ Continuous spectrum
$2$. Incandescent solids	$(B)$ Absorption spectrum
$3$. Fraunhofer lines	$(C)$ Band spectrum
$4$. Electric arc between iron rods	$(D)$ Emission spectrum

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Match the appropriate pairs from List-$I$ and List-$II$:
List-$I$ List-$II$
$1$. Nitrogen molecules $(A)$ Continuous spectrum
$2$. Incandescent solids $(B)$ Absorption spectrum
$3$. Fraunhofer lines $(C)$ Band spectrum
$4$. Electric arc between iron rods $(D)$ Emission spectrum

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