Final answer:
A substance with a pH of 3 is 4 times more acidic than pure water.
Step-by-step explanation:
The pH scale is used to measure the acidity or alkalinity of a substance. A pH of 7 is considered neutral, while a pH below 7 is acidic.
So, if the pH of a substance reads 3, it is 4 times more acidic than pure water, which has a pH of 7.