(A): The mole fraction of argon in air is 0.95
(R): The volume percentage of all noble gases in air is equal to unity 

Options

A. Both A & R are true, R is the correct explanation of A
B. Both A & R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer

To solve the assertion and reason question, we will analyze both statements step by step.

**Step 1: Analyze the Assertion**
- The assertion states: "The mole fraction of argon in air is 0.95."
- The mole fraction is defined as the ratio of the number of moles of a component to the total number of moles in the mixture. A mole fraction of 0.95 for argon would imply that 95% of the air is argon.
- However, this is incorrect because the actual concentration of argon in the atmosphere is around 0.93% by volume, which corresponds to a mole fraction of approximately 0.0093, not 0.95.
- Therefore, the assertion is **false**.

**Step 2: Analyze the Reason**
- The reason states: "The volume percentage of all noble gases in air is equal to unity."
- Noble gases present in the atmosphere include helium, neon, argon, krypton, and xenon. However, the total volume percentage of these noble gases in the air is approximately 1% (not 100% or unity).
- Therefore, the reason is also **false**.

**Step 3: Conclusion**
- Since both the assertion and the reason are false, we can conclude that the statement is incorrect. The assertion is false, and the reason is also false.

### Final Answer
- The assertion is false, and the reason is false.