Choose the alkali metal with the highest reactivity among the following.

Alkali metals are powerful reducing agents because

Caesium is used in

Which one on reaction with $NaOH$ solution gives inflammable gas?

Excess of $Na^+$ ions in our system causes:

Fill in the blanks:
$(1)$ Lithium on reaction with nitrogen present in air is denoted by .....
$(2)$ Potassium gives ...... colour in oxidizing flame.
$(3)$ ....... and ........ metals are used in photoelectric cells.
$(4)$ When alkali metal dissolves in ammonia,it produces a blue-coloured solution. This colour is due to .......