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PH is the index of acidity or neutrality or alkalinity (base nature) of a compound - a solution.
its range is 0 to 14.  pH of 7 means the solution is neutral.  pH of 0 means strong acid. pH of 14 means strong base.  Solutions with a pH from 0 to 7 exhibit acidic properties.
solutions from 7 to 14 have alkaline properties.
pH is actually a measure of the concentratio n of hydrozen ions.

It is defined as the negative common logarithm of the concentration of hydrogen ions [H+] in moles/litre:              pH = log [H+].  ( base of logarithm 10)
The hydrogen ionic activity is interesting in chemistry - in the study of equilibria.

P H is used in photographic development and bleaching activites. A photographic paper's longevity  depends on its pH

PH is defined as a negative logarithm of h+ ion concentration.

it is used to test whether the substance or solution is acidic or basic.
p H scale determines it. invented by sourenson.

if it ranges from 0-7 it is acidic
if it is exactly 7      it is neutral
if it ranges fron 7-15 it is basic