You're asking about substances that generate hydrogen ions (H+) when dissolved in water. These substances are called acids.

Here's why:

* Acids are substances that donate hydrogen ions (H+) when dissolved in water. This is why they are often described as having a sour taste and can react with bases to form salts and water.

Examples of acids:

* Hydrochloric acid (HCl): When dissolved in water, HCl dissociates into H+ and Cl- ions.

* Sulfuric acid (H2SO4): When dissolved in water, H2SO4 dissociates into 2H+ and SO4(2-) ions.

* Acetic acid (CH3COOH): When dissolved in water, acetic acid partially dissociates into H+ and CH3COO- ions.

Important Note: The strength of an acid is determined by how readily it donates hydrogen ions. Strong acids like HCl dissociate almost completely in water, while weak acids like acetic acid only partially dissociate.