(a) Nitric oxide turns brown in air. Why ?
(b) Copper dissolves in `HNO_3` but not in `HCl`. Why ?

Answer

(a) `N_(2)+3H_(2)overset(500^(circ)C,200atm.)underset("Iron oxide"+K_(2)O&Al_(2)O_(3))to2NH_(3)`" " ("4mole gases"(`N_(2)`and `H_(2))` "forms two mole" `NH_(3)`
(b) `2NO+O_(2)to 2NO_(2)` (Brown)
(c) Copper is placed below hydrogen in electrochemical series and does not liberate `H_(2)` from acid. However, `HNO_(3)` oxidises copper due to its strong oxidising nature.
`3Cu+8HNO_(3)("dil".) to 3Cu (NO_(3))_(2)+4H_(2)O+2NO`
(d) `Pb(NO_(3))_(2)overset(Delta)toN_(2)O_(4)overset(Delta)toNO_(2)uarr (Brown)`

Explanation

NA