What are the metal ions present in carnallite?

Give brief information on the atomic and ionic radius of alkali metals (Group $I$).

Write balanced chemical equations for the reactions between:
$(a)$ $Na_{2}O_{2}$ and water
$(b)$ $KO_{2}$ and water
$(c)$ $Na_{2}O$ and $CO_{2}$

Which of the following is the strongest reducing agent?

The white precipitate $(Y)$, obtained on passing a colourless and odourless gas $(X)$ through an ammoniacal solution of $NaCl$, loses about $37 \%$ of its weight on heating and a white residue $(Z)$ of basic nature is left. Identify $(X)$, $(Y)$, and $(Z)$ from the following sets.

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: