Question

When a student added universal indicator solution to one of the following chemicals, its colour changed to navy blue. The chemical is most likely to be :
(1) lemon juice
(2) milk of magnesia
(3) vinegar
(4) tomato juice

Answer 1

A Base turns the red litmus to blue or any color in the blue-violet region depending upon the pH range of the base. Milk of magnesia or magnesium hydroxide is a base, that's why it turns the red litmus to navy blue.

Hence, the correct answer is option 2.