pH: Definition: pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of asolutionAqueous 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. (taken from Chemistry)

In order to begin with pH Levels we will first watch this video.

Extension: Here are some additional sites with more information about pH: