Question

Given the reaction:
Ba(OH)2(aq) + H2SO4(aq) -->BaSO4(s) + 2 H2O(l) + energy
As the barium hydroxide solution is added to the solution of sulfuric acid, the electrical conductivity of the acid solution decreases because the
(1) volume of the reaction mixture increases
(2) temperature of the reaction mixture decreases
(3) concentration of ions increases
(4) concentration of ions decreases

Answer 1

The conductivity would decrease because the concentration of ions decreases.

As barium hydroxide, a solution is added to sulphuric acid, the Barium ions replace the hydrogen ions to form a precipitate.  An insoluble solid doesn't contribute ions and as such the forming of the solid barium hydroxide would mean a decrease in the concentration of the ions.