Write the molecular formula of Marshall's acid.

When an inorganic compound reacts with $SO_2$ in an aqueous medium,it produces $(A)$. $(A)$ on reaction with $Na_2CO_3$ gives compound $(B)$,which with sulphur,gives a substance $(C)$ used in photography. Compound $(C)$ is:

Statement $(A)$ Sulphur vapour is paramagnetic. Statement $(B)$ Reaction of dil. $HCl$ with finely divided iron forms $FeCl_3$ and $H_2$ gas. The correct answer is

Write the conditions to maximize the yield of $H_2SO_4$ by Contact process.

In the preparation of sulphuric acid from sulphur dioxide in the lead chamber process,what substance is used as a catalyst?

In the contact process for the production of $H_2SO_4$,which catalyst is required to convert $SO_2$ into $SO_3$?