When 0.1 mole of an acid is added to 2 lit of a buffer solution, the pH of the buffer decreases by 0.5. The buffer capacity of the solution is

0.5 change in PH occurs by adding 0.1 mole of an acid to 2 litre of buffer solution.1 change in PH occurs by adding 0.1 mole x 2 mole of an acid to 2 litre of buffer solution.1 change in PH occurs by adding 0.1×22=0.1mole of an acid to 1 litre of buffer solution.