Which of the following source materials generate $SO_2$ that is used in the contact process?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : Both rhombic and monoclinic sulphur exist as $S_8$ while oxygen exists as $O_2$.
Reason $(R)$ : Oxygen forms $p \pi-p \pi$ multiple bonds with itself and other elements having small size and high electronegativity like $C, N$,which is not possible for sulphur.
In the light of the above statements,choose the most appropriate answer from the options given below:

$V_2O_5$ is useful as a catalyst in:

Rhombic sulphur has the following structure:

Which of the following is acidic?

Which of the following hydrides is the most acidic?