Observe the diagram and answer the following.
$(a)$ Which element plays an important role in the opening and closing of stomata?

(C) The element that plays an important role in the opening and closing of stomata is Potassium $(K^+)$.
$1$. During the opening of stomata,$K^+$ ions are actively transported from the surrounding subsidiary cells into the guard cells.
$2$. This accumulation of $K^+$ ions lowers the water potential inside the guard cells.
$3$. Due to the lower water potential,water moves from the surrounding cells into the guard cells via osmosis.
$4$. As water enters,the guard cells become turgid and expand,causing the stomatal pore to open.
$5$. Conversely,the exit of $K^+$ ions leads to the loss of water from the guard cells,making them flaccid and causing the stomata to close.