Which of the following is called white vitriol?

$2Na_2O \overset{400 \ ^oC}{\rightleftharpoons} A + 2Na$
$A + SO_2 \to Na_2SO_4$
$A + CO \to Na_2CO_3$
In the above reaction,$A$ is:

Which of the following is the strongest reducing agent?

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

List-$I$	List-$II$
$(a)$ $NaOH$	$(i)$ Acidic
$(b)$ $Be(OH)_{2}$	$(ii)$ Basic
$(c)$ $Ca(OH)_{2}$	$(iii)$ Amphoteric
$(d)$ $B(OH)_{3}$
$(e)$ $Al(OH)_{3}$

Choose the most appropriate answer from the options given below :

When $CO$ is passed over solid $NaOH$ heated to $200\,^{\circ}C$,it forms

The most soluble bicarbonate is