Name a solution which gives nitrogen dioxide with copper.

When nitric acid is prepared by the action of concentrated sulphuric acid on potassium nitrate, what is the special feature of the apparatus used.

Potassium nitrate is prepared from KOH and nitric acid. State the type of reaction involved.

State the conc. acid which will oxidise sulphur directly to H₂SO₄. Write the equation for the same.