(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). Identify (A) and (B). Writen chemical reactions involved.
(b) Drawn structure of `XeOF_(4).`

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`