Question

Which of the following is an acid-base indicator?
A. Vinegar
B. Turmeric
C. Lime water
D. Baking soda

Answer 1

In chemistry indicators are chemical compounds that indicate the presence or absence of another compound by a sign of visual change like a change of color of the solution. Such as for acidic and basic solutions. There are some examples of indicators are methyl blue, phenolphthalein, etc.

Complete step by step answer:
An acid-base indicator is a pH indicator of a solution of several compounds. This solution of universal indicator exhibits several color changes from the range of 1-14 in the pH scale. This pH indicator indicates the acidity or basicity of the solution. For example, the color of the cabbage juice is red because it is an acidic solution.
According to the pH scale if any solution is with a lower pH value (less than 7) is acidic in nature, and if the pH of the solution is higher (greater than 7) then the solution is basic. For pure water, the pH of the solution is 7.
There is some example of indicators with the pH range as follows,

Phenolphthalein	8.2-10
Bromothymol Blue	6.0-8.4
Methyl red	4.2-6.2
Phenol red	6.8-8.4

Now when the color of the solution changes to red then the dilution is acidic. And when the color is blue it is called a basic solution.
Now among the given options, turmeric changes its color to reddish-brown in basic solution. But in the case of the acid solution, the color of turmeric remains the same. So, it can be used as an indicator.

So, the correct option is B.

Note: Phenolphthalein is generally used as an indicator of acid-base titrations. It turns colorless when added to acid and pink when added to basic solutions. Caustic soda is a strong base and will ionize more when phenolphthalein is added to it.