Answer:
Step-by-step explanation:
Lithium, Potassium and Sodium follow each other in that order when it comes to reactivity.
Succinctly put, Lithium is the most reactive. Potassium is more reactive and Sodium is the least reactive.
Also, for Calcium, Strontium and Barium. It is the least reactive in this order.
Strontium, Barium, Calcium
That is, Strontium is more reactive than Barium, which is more reactive than Calcium. Calcium is the least reactive of the 3