Question 1

The measure of concentration of H₃O⁺ ions

pH is defined as a measure of the concentration of hydronium ions (H₃O⁺) in a solution, which indicates how acidic or basic that solution is.

A) The measure of concentration of H₃O⁺ ions

This option is correct as pH specifically quantifies the concentration of hydronium ions in a solution. The pH scale is logarithmic and inversely related to the concentration of H₃O⁺ ions, making this definition accurate.

B) The measure of concentration of hydrogen ions

While the pH is related to the concentration of hydrogen ions (H⁺), it is more accurately represented by the concentration of hydronium ions (H₃O⁺) in solution. Hydrogen ions exist in water primarily as hydronium ions, so this option is misleading.

C) The measure of concentration of H₂O molecules

This option is incorrect because pH does not measure the concentration of water molecules (H₂O). Rather, it focuses on the concentration of ions in solution, specifically hydronium ions, which are formed when hydrogen ions associate with water.

D) None of the above

This option is incorrect because option A provides a valid definition of pH. Thus, stating "none of the above" is not accurate as there is a correct choice present.

Conclusion

The definition of pH as the measure of concentration of H₃O⁺ ions is fundamental to understanding acidity and basicity in solutions. Options B and C misrepresent the concept, while option D dismisses the correct answer. Therefore, option A is the only accurate choice that correctly defines pH.