Give reasons for the following :
(a) Sulphuric acid forms two types of salts with NaOH,
(b) Red brown vapours are produced when concentrated sulphuric acid is added to hydrogen bromide,
(c) A piece of wood becomes black when concentrated sulphuric acid is poured on it,
(d) Brisk effervescence is seen when oil of vitriol is added to sodium carbonate.
Sulphuric acid forms two types of salt when reacted with sodium hydroxide in different conditions.