(a) When concentrated sulphuric acid was added to an unknown salt present in a test tube a brown gas (A) was evolved . This gas intensified when copper turnings were added to this test tube . On cooling, the gas (A) changed into a colourless solid (B) .
(i) Identify (A) and (B).
(ii) Write the structures of (A) and (B).
(iii) Why does gas (A) change to solid on cooling ?
(b) Arrange the following in the decreasing order of their reducing character :
HF , HCl , HBr , HI
(c) Complete the following reaction :
`XeF_(4) + SbF_(5) to `

Explanation

(a) `2NaNO_(3)+H_(2)SO_(4)overset(Delta)tounderset(("colourless"))(2HNO_(3))+Na_(2)SO_(4)`
`4HNO_(3)overset(Delta)tounderset(("nitrogen dioxide"))underset(("Brown"))underset((A))(2NO+_(2))+O_(2)+2H_(2)O`
`underset("turnings")underset("Copper")(Cu)+HNO_(3)overset(Delta)toCu(NO_(3))_(2)+underset((A))(2NO_(2))+2H_(2)O`