When $Na$ is heated at $300\,^oC$,it forms $X$. It absorbs $CO_2$ to form $Na_2CO_3$ and $Y$. What is $Y$?

Give brief explanations on hydroxides of alkali metals.

What type of oxides do alkali metals form? Discuss some of the physical properties of these oxides.

Explain how industrial production of sodium hydroxide is carried out by the Castner-Kellner cell.

Write the decreasing order of hydration enthalpy of alkali metal ions.

Fill in the blanks:
$(1)$ ......... method is used to prepare sodium carbonate.
$(2)$ Sodium carbonate exists as .........
$(3)$ Sodium chloride is commonly known as .........
$(4)$ Sodium chloride melts at ......... temperature.