Why are alkali metals not found in nature ?

Hello shashank. Apology for the delay. Here is the solution.

Alkali metals are naturally occurring, but not as pure elements.
This is because the alkali metals are extremely reactive, the easily react with air and water and can only be extracted from the resulting compounds by artificial methods.
Also s they have only one electron in their valence shell. And, they have the largest atomic radii and highest ionisation enthalpies. So, they have a strong tendency to lose their valence electron and change to unipositive ion.
They are generally found as salts.