Chile saltpetre is

Which of the following statements is $CORRECT$?

Assertion $A$: Alkali metal elements impart characteristic colors to the flame in a flame test.
Reason $R$: They have very low ionization enthalpy.

Write down the biological importance of $Na$ and $K$ in the human body and give a brief note on the sodium-potassium pump.

The correct order of conductivity of ions in water is

$A$ substance $X$ is a compound of an element of group $IA$. The substance $X$ gives a violet colour in flame test. $X$ is