Consider the following statements regarding the properties of Acids and Bases:

I. Both acidic and basic solutions conduct electricity because they produce ions in aqueous solutions.

II. Antacids are weak bases that neutralize excess stomach acid.

III. Acidic solutions turn red litmus paper blue.

IV. Phenolphthalein remains colourless in acidic solution but turns pink in basic solution.

V. Tooth decay starts when the pH of the mouth is above 8.5.

Which of the above statements are INCORRECT?