Why are alkali metals not found in nature?

Lithium shows similarities to magnesium in the chemical behaviour. What is the cause of this similarity?

What is the nature of lithium compounds?

Group 1 elements are called alkali metals. Why?

Why caesium can be used in photoelectric cell while lithium can not be?

In aqueous solution, Li⁺ ion has lowest mobility. Why?

Lithium has highest ionisation energy in group 1 elements, yet it is strongest reducing agent. Comment.

The softness of group 1 elements increases down the group with increasing atomic number. Give reason. 

Which is the most reactive alkali metal and why?