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 the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that 10 ml of liquid A mixed with 20 ml of liquid B results in a total volume of 30 ml.
- This means that when these two liquids are mixed, there is no volume contraction or expansion, which is a characteristic of ideal solutions.

2. **Understanding the Reason (R)**:
- The reason states that A and B will form an ideal solution.
- An ideal solution is defined as a homogeneous mixture of substances whose physical properties (like vapor pressure, boiling point, etc.) are linearly related to the pure components.
- For a solution to be considered ideal, the total volume after mixing should equal the sum of the individual volumes of the components (VA + VB).

3. **Calculating the Total Volume**:
- Given:
- Volume of liquid A (VA) = 10 ml
- Volume of liquid B (VB) = 20 ml
- Total volume after mixing = VA + VB = 10 ml + 20 ml = 30 ml.
- This confirms that the total volume is indeed 30 ml, which is consistent with the behavior of an ideal solution.

4. **Conclusion**:
- Since the total volume of the solution is equal to the sum of the individual volumes, this supports the assertion that A and B form an ideal solution.
- Therefore, both the assertion (A) and the reason (R) are correct, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and the reason is a correct explanation of the assertion.

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