Which of the following statements regarding the application of electrical conduction via gases is/are correct?…

To solve this question, let’s break down each application of electrical conduction through gases:

1. Analysis of the Statements

• (i) The identification of gases: This is correct. When a gas is subjected to a high-voltage discharge at low pressure, it emits a characteristic spectrum (spectral lines). By analyzing these lines (spectroscopy), scientists can identify the specific gas present.
• (ii) Lighting/fluorescent tubes: This is correct. Fluorescent tubes and neon signs work by passing an electric current through a gas or vapor (like mercury vapor or neon). The gas becomes ionized, emits ultraviolet light, which then strikes a phosphor coating to produce visible light.
• (iii) Photocells: This is incorrect in the context of electrical conduction through gases. Photocells (or photoelectric cells) operate based on the photoelectric effect, where light hitting a metal surface causes the emission of electrons. While some gas-filled photocells exist, the fundamental principle of a photocell is the interaction of light with a solid surface, not the conduction of electricity through a gas as the primary mechanism.
• (iv) Cathode ray oscilloscope (CRO) / T.V. tubes: This is correct. These devices rely on the production of a beam of electrons in a vacuum or low-pressure gas environment. The movement of these electrons (cathode rays) is controlled by electric or magnetic fields to display images or waveforms.

2. Evaluating the Options

Based on our analysis, statements (i), (ii), and (iv) are the correct applications of electrical conduction through gases.

• Option A includes (iii), which is incorrect.
• Option B includes (i), (ii), and (iv), which matches our findings.
• Option C includes (iii), which is incorrect.
• Option D includes (iii), which is incorrect.

3. Conclusion

Exam Tip: When you see questions about "conduction through gases," always look for keywords like discharge tubes, ionization, spectral lines, or cathode rays. If you see "photoelectric effect," remember that it is primarily a surface phenomenon involving solid metals, not gas conduction.