A change in pH of 1.0 unit indicates that:. 1. the molarity of H changes by one order of magnitude.
2. the volume of H in a solution changes by an order of magnitude.
3. the acid or base content decreases or increases by 1.0 M.
4. the acid or base content decreases or increases by 0.1 M.
5. the salt content decreases or increases by 1.0 M.

The correct answer is - option 1. the molarity of H changes by one order of magnitude.

Explanation:

pH is dependent on the concentration of H+ not on the volume of H+ or the salt content.  The molarity of H+ changes by one order of magnitude with the change in pH of 1.0 unit that can be an increase or decrease in molar concentration by one order of magnitude or factor of 10.

Order of magnitude refers to the factor of ten or powers of ten. A change in the order is equal to the change of the exponent changes by ± 1