The number of molecules of water needed to convert one molecule of ${\mathrm{P}}_2{\mathrm{O}}_5$ into Ortho phosphoric acid is:

The following acids have been arranged in order of decreasing acid strength. Identify the correct order.

$\mathrm{ClOH}\left(\mathrm{I}\right), \mathrm{BrOH}\left(\mathrm{II}\right), \mathrm{IOH}\left(\mathrm{III}\right)$

A black sulphide when treated with ozone becomes white.