Acid and base testing is a method used to determine the pH level of a substance, indicating whether it is acidic, basic (alkaline), or neutral. This is often done using indicators like litmus paper, pH paper, or liquid indicators such as phenolphthalein and bromothymol blue. Acids typically have a pH less than 7 and turn blue litmus paper red, while bases have a pH greater than 7 and turn red litmus paper blue. Neutral substances, like pure water, have a pH of 7 and do not change the color of litmus paper. These tests are commonly used in laboratories, schools, and even at home to analyze substances like lemon juice, baking soda solution, vinegar, and soap. Acid and base testing helps in understanding chemical properties and is important in fields like chemistry, biology, medicine, and environmental science.