(a) Exchange of ions between both the reactants takes place; therefore, it is an example of double displacement reaction. Since, precipitate of barium sulphate forms, it is also a precipitation reaction.
(b) The balanced chemical reaction is given as follows:
Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (aq)
(c) Reaction will not take place if the reactants are in solid state.
(d) Double displacement reaction takes place.
(e) Another reaction of same type is given as follows:
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)