Answer: 3.54
Explanation:-
pH is the measure of acidity or alkalinity of a solution.
It is measured by taking negative logarithm of hydrogen ion concentration.
[tex]pH=-\log [H^+][/tex]
Given: [tex][H^+]=2.87\times 10^{-4}[/tex]
[tex]pH=-\log (2.87\times 10^{-4})[/tex]
[tex]pH=3.54[/tex]
As pH is 3.54 which is less than 7, the substance is acidic in nature.