pH stands for potential of Hydrogen. It represents the ratio of Hydronium ions (H3O) to Hydroxide ions (OH). It is a measure of acidity and alkalinity of a solution. The pH scale usually ranges from 0 to 14. Aqueous solutions at 25°C with a pH less than seven are acidic, while those with a pH greater than seven are basic or alkaline. A pH level of is 7.0 at 25°C is defined as 'neutral' because the concentration of H3O+ equals the concentration of OH− in pure water.