Bileah acid or base refers to the acidity or alkalinity of a substance. Acids release hydrogen ions (H+) when dissolved in water, while bases release hydroxide ions (OH-). The pH scale measures the concentration of hydrogen ions in a solution, with a pH of 7 indicating neutrality, values below 7 indicating acidity, and values above 7 indicating basicity. Acids have a sour taste, react with metals to produce hydrogen gas, and turn litmus paper red. Bases have a bitter taste, feel slippery, and turn litmus paper blue.