Dear User,
Kidney balances the pH of the body by excretion of waste products. It maintains the acid base by excreting hydrogen ions into the urine and then reabsorb bicarbonate from the urine.
Lungs maintain the acid base balance by maintaining the rate of breathing. More the CO2 in the blood, more will be its acidity. Faster breathing means more amount of exhalattion of CO2 and so less in blood i.e. decreased acidity.