What is formed by the reaction of phosphorus pentachloride with concentrated sulfuric acid?

Explain the oxoacids of sulfur.

Which of the following activities results in the formation of oleum in the manufacture of sulphuric acid by the contact process?

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

For the preparation of sodium thiosulphate by the "Springs reaction",the reactants used are