Here's why:

* Potassium (K) is a highly reactive alkali metal.

* Water (H₂O) contains hydrogen.

* When potassium reacts with water, it displaces hydrogen from the water molecules.

* This produces potassium hydroxide (KOH) and hydrogen gas.

The chemical equation for the reaction is:

2K + 2H₂O → 2KOH + H₂

The "pop" sound is caused by the rapid combustion of the hydrogen gas in the air.