Which of the following is called white vitriol?

Which of the following oxides is not expected to react with sodium hydroxide?

Thermal decomposition of lithium nitrate gives:

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 oxides is highly basic?

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