Question

lithium and sodium are considered as active metals. why?

Answer 1

Because they are very reactive:
When put in water they react vigorously releasing large amounts of energy in the form of heat. 

Answer 2

Answer:

to attain stability

Explanation:

both lithium and sodium have one electron each in their outermost shell.

Hence,they react vigorously to lose and electron to attain the nearest configuration.......

i.e

1.lithium loses one electron to attain duplet configuration.

2.sodium loses one electron to attain octet configuration.