What type of oxides are formed when non-metals combine with oxygen?

Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it,as shown in the figure below.
$(a)$ What will be the action of the gas on
$(i)$ dry litmus paper?
$(ii)$ moist litmus paper?
$(b)$ Write a balanced chemical equation for the reaction taking place.

An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

Give reasons: $Sodium$,$potassium$,and $lithium$ are stored under oil.

Which of the following pairs will give displacement reactions?

Samples of four metals $A$,$B$,$C$ and $D$ were taken and added to the following solutions one by one. The results obtained have been tabulated as follows.

Metal	Iron $(II)$ sulphate	Copper $(II)$ sulphate	Zinc sulphate	Silver nitrate
$A$	No reaction	Displacement	No reaction	Displacement
$B$	Displacement	Displacement	No reaction	Displacement
$C$	No reaction	No reaction	No reaction	Displacement
$D$	No reaction	No reaction	No reaction	No reaction

Use the table above to answer the following questions about metals $A$,$B$,$C$ and $D$:
$(i)$ Which is the most reactive metal?
$(ii)$ What would you observe if $B$ is added to a solution of Copper $(II)$ sulphate?
$(iii)$ Arrange the metals $A$,$B$,$C$ and $D$ in the order of decreasing reactivity.