Which one of the following dissolves in hot concentrated $NaOH$ solution?

State the reasons for the following:
$(a)$ Why is a solution of $Na_{2}CO_{3}$ alkaline?
$(b)$ Why are alkali metals prepared by the electrolysis of their fused chlorides?
$(c)$ Why is sodium found to be more useful than potassium in biological systems?

Which of the following reactions is not correct?

Match the List-$I$ with List-$II$.

List-$I$ (Metal)	List-$II$ (Emitted light wavelength $(nm)$)
$A. Li$	$I. 670.8$
$B. Na$	$II. 589.2$
$C. Rb$	$III. 780.0$
$D. Cs$	$IV. 455.5$

Choose the most appropriate answer from the options given below:

The nitrate of which metal does not give nitrogen dioxide on strong heating?

Which alkali metal carbonate decomposes on heating to liberate $CO_2$ gas?