Hint: An indicator is a chemical substance that is used to determine the nature of any given substance, it means by the use of an indicator we can ensure that a given substance is an acid or a base.
Complete step by step answer: Indicators usually show the different effects of color and odor in the presence of an acid as well as in the presence of a base, which is different from their natural behavior. In the given question all the above options are examples of natural indicators and show the following effects in the acidic and basic solution: -Turmeric in the aqueous form presents in the natural yellow color in both acidic and neutral solution but shows red color in the presence of basic solution. -Cabbage in the form of juice is used as an indicator where it shows pink color in the presence of an acid and blue or green color in the presence of basic solution. -Onion is also known by the name of olfactory indicator which shows acidity or basicity by changing its smell or odor only. Onion losses its smell in the basic medium. All given compounds are used as an indicator, so one option is correct regarding the statement of the question. So, the correct answer is “Option D”.
Note: Here some of you may think that onion is not an indicator because it doesn’t change its color, so that assumption is wrong because it shows indication by changing its odor, not the color.