The essential constituent of an amalgam is:

In which of the following is sodium metal stored?

Zinc $(II)$ ion on reaction with $NaOH$ first gives a white precipitate which dissolves in excess of $NaOH$ due to the formation of:

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.

Baking soda is

Arrange the following compounds in the increasing order of their thermal stability. Identify the correct sequence.
$I - K_2CO_3, II - MgCO_3, III - CaCO_3, IV - BeCO_3$