A: Gases are insulators at ordinary pressure but they start conducting at very low pressure.
R: At low pressures, ions have a chance to reach their respective electrodes and constitute a current but at ordinary pressures, ions undergo collision with gas molecules and recombination.

Options

A. If both Assertion & Reason are true and the reason is the correct explantion of the assertion , then mark (1)
B. if both Assertion & Reason are true but the reason is not the correct explantion of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To analyze the assertion and reason provided in the question, we can break down the explanation step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that "Gases are insulators at ordinary pressure but they start conducting at very low pressure."
- At ordinary pressure, gas molecules are densely packed, which means that there are many collisions between gas molecules. This prevents the free movement of charge carriers (like ions), making the gas behave as an insulator.

2. **Understanding the Reason:**
- The reason states that "At low pressures, ions have a chance to reach their respective electrodes and constitute a current but at ordinary pressures, ions undergo collision with gas molecules and recombination."
- At low pressures, the density of gas molecules is reduced, leading to fewer collisions between ions and gas molecules. This allows ions to travel freely towards the electrodes, enabling the flow of electric current.

3. **Connecting Assertion and Reason:**
- The assertion is correct because gases do behave as insulators at ordinary pressures due to the high frequency of collisions.
- The reason is also correct because, at low pressures, the reduced number of collisions allows ions to reach the electrodes and contribute to current flow.

4. **Conclusion:**
- Both the assertion and the reason are correct, and the reason correctly explains the assertion. Therefore, the correct choice is that both the assertion and reason are true, and the reason is a valid explanation for the assertion.

### Final Answer:
Both the assertion and reason are correct, and the reason correctly explains the assertion.

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