Name the monovalent metallic cation involved in opening and closing of stomata

Explanation

### Step-by-Step Solution

1. **Understanding Stomata**: Stomata are small pores located on the surface of leaves that facilitate gas exchange and transpiration in plants.

2. **Role of Guard Cells**: The opening and closing of stomata is regulated by guard cells. These cells surround each stoma and control its size.

3. **Mechanism of Opening**: When guard cells absorb water, they become turgid (swollen). This turgidity causes the thin outer walls of the guard cells to push outward, which in turn pulls the thicker inner walls apart, resulting in the opening of the stomata.

...