Which chemical is noted for causing a decrease in pH?

The chemical that is noted for causing a decrease in pH is sulfuric acid. When sulfuric acid is introduced into a solution, it dissociates to release hydrogen ions (H+). The presence of these hydrogen ions increases the acidity of the solution, which in turn lowers the pH level.

In comparison, sodium hydroxide is a strong base that would increase pH, making a solution more alkaline rather than acidic. Ammonium nitrate, while it can affect pH when dissolved, does not inherently cause a significant decrease in pH as sulfuric acid does. Lastly, calcium carbonate acts as a buffering agent that can neutralize acids, leading to an increase in pH when reacting with acidic substances. Therefore, sulfuric acid is the chemical specifically recognized for its ability to decrease pH effectively.