A beam of ultraviolet light of all wavelength passes through hydrogen gas at room temperature, in the x-direction. Assume that all photons emitted due to electron transitions inside the gas emerge in the y-direction. Let A and B denote the lights emerging from the gas in the x-and y-directions respectively.
(i) Some of the incident wavelengths will be absent in A
(ii) Only those wavelengths will be present in B which are absent in A
(iii) B will contain some visible light
(iv) B will contain some infrared light

Options

A. Some of the incident wavelengths will be absent in A
B. Only those wavelngth will be present in B which are absent in A
C. B will contain some visible light
D. B will contain some infrared light

Explanation

To analyze the question regarding the behavior of ultraviolet light passing through hydrogen gas, let's break down the statements step by step:

### Step-by-Step Solution:

1. **Understanding the Incident Light:**
A beam of ultraviolet light (which contains a spectrum of wavelengths) is directed towards hydrogen gas. This light travels in the x-direction.

**Hint:** Remember that ultraviolet light has a higher energy than visible light, which means it can excite electrons in hydrogen atoms.

2. **Electron Excitation:**
When the ultraviolet light interacts with the hydrogen gas, some of the photons are absorbed by the hydrogen atoms. This absorption causes the electrons in the hydrogen atoms to get excited to higher energy levels.

**Hint:** The energy of the absorbed photons corresponds to the energy difference between the ground state and the excited state of the hydrogen atom.

3. **Photon Emission:**
After a short time, the excited electrons will return to their original (ground) state, emitting photons in the process. These emitted photons will travel in the y-direction.

**Hint:** The emitted photons will have specific wavelengths corresponding to the energy transitions of the electrons in the hydrogen atom.

4. **Analyzing Statement (i):** "Some of the incident wavelengths will be absent in A."
This statement is true because the wavelengths of the ultraviolet light that are absorbed by the hydrogen atoms will not be present in the light that emerges in the x-direction (A).

**Conclusion for (i):** True.

5. **Analyzing Statement (ii):** "Only those wavelengths will be present in B which are absent in A."
This statement is false. While some wavelengths absorbed by hydrogen will result in emitted photons, not all absorbed energy results in photon emission. Some energy may be lost as heat or through other processes. Thus, B may contain wavelengths that are not simply the ones absorbed from A.

**Conclusion for (ii):** False.

6. **Analyzing Statement (iii):** "B will contain some visible light."
This statement cannot be conclusively determined without specific data about the transitions of the hydrogen atom. The emitted light in the y-direction (B) could potentially include visible light, but it is not guaranteed.

**Conclusion for (iii):** Cannot be determined.

7. **Analyzing Statement (iv):** "B will contain some infrared light."
Similar to statement (iii), we cannot definitively say that B will contain infrared light without knowing the specific transitions that occur.

**Conclusion for (iv):** Cannot be determined.

### Final Conclusion:
- The only statement that can be confirmed as true is (i).
- Statements (ii), (iii), and (iv) cannot be definitively confirmed.

### Summary of Answers:
- (i) True
- (ii) False
- (iii) Cannot be determined
- (iv) Cannot be determined