Gypsum is not used to reduce soil pH because it will displace the soil H+ but there's no means of extracting the H from the soil. So the pH of the soil remains the same.
If plants are given nitrogen fertilizer, then they will grow taller. ... Factors in an experiment that a scientist PURPOSELY Changes (manipulated) Control Group ... to test various amounts of fertilizer to find out what amount makes plants grow
When an electric current is passed through acidified water, it decomposes to give hydrogen and oxygen gas. The hydrogen gas is obtained at the cathode and the oxygen gas is obtained at the anode