Acid and bases both are the substances that cause corrosion. They can be differentiated on the basis of properties and pH.
If the pH is less than 7.0 the solution is acidic while if its value is greater than 7.0 it is the basis solution.
Examples:
Acid
Acetic acid has pH value 2.4
Sulphuric acid has pH value 0 for 1M solution
Base
pH of ammonia solution is 11