Here's why:

* Reactivity: Alkali metals are highly reactive and readily react with air and moisture.

* Kerosene as a Protective Layer: Kerosene acts as a protective layer, preventing the alkali metals from coming into contact with air and moisture, thus inhibiting oxidation and preserving them.

Examples of alkali metals preserved in kerosene:

* Lithium (Li)

* Sodium (Na)

* Potassium (K)

* Rubidium (Rb)

* Cesium (Cs)

Important Note: While kerosene is commonly used to preserve alkali metals, it's crucial to remember that it's a flammable liquid. Proper handling and storage procedures should always be followed.