2.7 describe the relative reactivates of the elements in Group 1

Lithium reacts a little, however, as you get further down the group they react more. For example (reactions with water)...

Lithium - lithium moves slowly around the container, fizzing, until it disappears (approx. 30 seconds).

Sodium - sodium moves quickly around the container, fizzing rapidly, until it disappears (approx. 20 seconds). 

Potassium - potassium fizzes and reacts vigorously until it disappears (approx. 5 seconds)