Question

Which of the following is a synthetic indicator?

• A. Turmeric
• B. Methyl orange
• C. Litmus solution
• D. Red cabbage extract

Hint:

Common synthetic indicators include methyl orange, phenolphthalein, and methyl red. Natural indicators are derived from plants or other natural materials.

Answer 1

The Correct Option is B

Step 1: Understand the difference between natural and synthetic indicators.
Indicators are substances that change colour with a change in pH. They can be obtained from natural sources or synthesized in the laboratory. 
Step 2: Analyze the origin of each of the given indicators.
 

• Turmeric:
  Turmeric is a common spice obtained from the turmeric plant. It acts as a natural pH indicator, turning yellow in acidic and neutral solutions and reddish-brown in basic solutions.
• Methyl orange:
  Methyl orange is an azo dye synthesized in the laboratory. It is a synthetic pH indicator that shows a colour change from red in acidic solutions to yellow in basic solutions, with a transition range of pH 3.1 to 4.4.
• Litmus solution:
  Litmus is a natural indicator obtained from lichens. It is commonly used in the form of litmus paper (red and blue) or as a solution. Blue litmus turns red in acidic solutions, and red litmus turns blue in basic solutions.
• Red cabbage extract:
  Red cabbage contains pigments called anthocyanins that change colour depending on the pH of the solution. It is a natural indicator, showing a range of colours from red in acidic solutions to green and yellow in alkaline solutions.

Step 3: Identify the synthetic indicator among the options.
Methyl orange is synthesized chemically in the laboratory, making it a synthetic indicator. Turmeric, litmus solution, and red cabbage extract are obtained from natural sources.