A: 10ml of liquid A mixed with 20ml of liquid B total volume of solution is 30 ml.
R: A and B will ideal solution.

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that when 10 ml of liquid A is mixed with 20 ml of liquid B, the total volume of the solution is 30 ml.
- This means that there is no volume contraction or expansion upon mixing the two liquids.

2. **Understanding the Reason (R)**:
- The reason states that liquids A and B will form an ideal solution.
- An ideal solution is formed when the intermolecular forces between the components (A and B) are similar to the intermolecular forces within the components themselves (A with A and B with B).
- In an ideal solution, the total volume of the solution is equal to the sum of the individual volumes of the components.

3. **Analyzing the Conditions for Ideal Solutions**:
- For A and B to form an ideal solution, the interactions between A and B must be similar to the interactions between A-A and B-B.
- If this condition is met, the volumes will add up without any contraction or expansion, which is what is observed here (10 ml + 20 ml = 30 ml).

4. **Conclusion**:
- Since the assertion is true (the total volume is indeed 30 ml) and the reason is also true (A and B can form an ideal solution under the right conditions), we conclude that both the assertion and reason are true.
- Furthermore, the reason correctly explains the assertion because it clarifies why the total volume remains unchanged.

### Final Answer:
Both the assertion and the reason are true, and the reason is the correct explanation of the assertion.

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