Match List-$I$ with List-$II$ :

List-$I$	List-$II$
$A$. $K$	$I$. Thermonuclear reactions
$B$. $KCl$	$II$. Fertilizer
$C$. $KOH$	$III$. Sodium potassium pump
$D$. $Li$	$IV$. Absorbent of $CO_2$

Choose the correct answer from the options given below :

Comment on each of the following observations:
$(a)$ The mobilities of the alkali metal ions in aqueous solution are
$Li^{+} < Na^{+} < K^{+} < Rb^{+} < Cs^{+}$
$(b)$ Lithium is the only alkali metal to form a nitride directly.
$(c)$ $E^{\circ}$ for $M^{2+}_{(aq)} + 2e^{-} \longrightarrow M_{(s)}$ (where $M = Ca, Sr$ or $Ba$) is nearly constant.

To which group do the following elements belong? Which of them has the highest metallic character?
$K, Na, Li, Rb$

Alkali metals dissolve in liquid ammonia to give a blue-colored solution if it is dilute. This blue color is due to which of the following?

Which of the following is an alkali metal?

Fill in the blanks:
$(1)$ Sodium hydroxide is also known as ......
$(2)$ The reaction of sodium amalgam with water produces ...... and ...... gas.
$(3)$ Sodium hydroxide on reaction with $CO_2$ produces ......
$(4)$ Sodium hydrogen carbonate is known as ......