What are the products formed when $Li_2CO_3$ undergoes thermal decomposition?

Which of the following is an alkali metal?

Sodium carbonate reacts with $SO_2$ in aqueous medium to give

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 .......

Select the correct statement from the following.

Which of the following methods is generally used for the extraction of alkali metals?