Crude sodium chloride obtained by crystallisation of brine solution does not contain

Fill in the blanks:
$(1)$ Among all alkali metals,.......... is a radioactive element.
$(2)$ The half-life of $^{223}Fr$ is ..........
$(3)$ Among all alkali metal ions,............ has the highest ionization enthalpy.
$(4)$ Alkali metals are identified by the ........... test.

Which of the following is not a product,when $RbO_2$ reacts with $H_2O$?

The dark red colour of bombs in fireworks is due to the presence of:

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

$Na + Al_2O_3$ $\xrightarrow{\text{High temperature}} X$ $\xrightarrow[\text{water}]{CO_2} Y$; compound $Y$ is