Regular use of which of the following fertilizers increases the acidity of soil ?

Regular use of ammonium-based fertilizers such as ammonium sulfate, ammonium nitrate, and urea can increase the acidity of soil. These fertilizers contain nitrogen in the ammonium form, which can release hydrogen ions (H⁺) into the soil as they undergo nitrification, a process that converts ammonium into nitrate. The increased concentration of hydrogen ions can lower the pH of the soil and make it more acidic.