Final answer:
During electrolysis of acidic water in Hoffman's apparatus, the pH increases due to the formation of hydroxide ions which combine with hydrogen ions, decreasing the hydrogen ion concentration and making the solution less acidic.
Step-by-step explanation:
The question asks what is the pH change of acidic water during electrolysis in Hoffman's apparatus. When acidic water undergoes electrolysis, hydroxide ions (OH-) are produced at the cathode. The increase in hydroxide ions in the solution can decrease the concentration of hydrogen ions because hydroxide ions will combine with hydrogen ions to form water.
This results in an increase in the pH of the solution, making it less acidic. Therefore, the correct answer is (b) The pH increases due to the formation of hydroxide ions.