[A]: Stomata open when guard cells have more `H^+` .
[R]: Increased `K^+` concentrations results in exo-osmosis in guard cells.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To analyze the statements given in the question, we need to evaluate both the assertion (A) and the reason (R) regarding the function of stomata and guard cells.

### Step-by-Step Solution:

1. **Understanding Stomata and Guard Cells**:
- Stomata are small openings found on the surfaces of leaves and stems that facilitate gas exchange (CO2 in and O2 out) and transpiration (loss of water vapor).
- Guard cells are specialized cells that flank each stoma and control its opening and closing.

2. **Assertion (A)**: "Stomata open when guard cells have more `H^+`."
- This statement is **incorrect**. Stomata do not primarily open due to an increase in hydrogen ions (`H^+`). Instead, they open when there is an increase in potassium ions (`K^+`) in the guard cells.

3. **Reason (R)**: "Increased `K^+` concentrations results in exo-osmosis in guard cells."
- This statement is also **incorrect**. Increased concentrations of potassium ions lead to the influx of water into guard cells (not exo-osmosis), causing them to swell and open the stomata. Exo-osmosis refers to the movement of water out of the cells, which occurs when potassium concentrations decrease.

4. **Conclusion**:
- Both the assertion (A) and the reason (R) are false. The opening of stomata is primarily due to the increase in potassium ions, which causes water to enter the guard cells, leading to their swelling and the opening of the stomatal pore.

### Final Answer:
- **Assertion (A)** is false.
- **Reason (R)** is false.