Answer : The pH value of an acid is below 7.
Explanation :
pH : It is defined as the negative logarithm of hydrogen ion or hydronium ion concentration.
Mathematically,
When the pH less than 7 then the solution is acidic and the concentration of hydrogen ion is greater than hydroxide ion.
When the pH more than 7 then the solution is basic and the concentration of hydrogen ion is less than hydroxide ion.
When the pH is equal to 7 then the solution is neutral and the concentration of hydrogen ion is equal to the hydroxide ion.
Hence, the pH value of an acid is below 7.