Which of the following is/are a natural indicator(s)?

Turmeric

The correct answer is option 1. Turmeric.

Turmeric is a natural indicator derived from the roots of the Curcuma longa plant. It contains a natural pigment called curcumin, which is responsible for its vibrant yellow color. Curcumin undergoes a reversible chemical change in response to changes in pH, making turmeric a suitable indicator for acid-base reactions.

In acidic solutions, curcumin remains in its protonated form and exhibits a yellow color. However, in basic solutions, curcumin undergoes deprotonation, resulting in a structural change that causes it to absorb light differently and appear red or orange.

This color change is due to the presence of functional groups within curcumin that can either accept or donate protons depending on the pH of the solution. Specifically, curcumin contains phenolic hydroxyl groups (-OH) and keto-enol tautomers, which are susceptible to protonation and deprotonation reactions.

When turmeric is used as an indicator, the observed color change provides information about the pH of the solution being tested. For example, in the presence of an acid, the solution will remain yellow, while in the presence of a base, the solution will turn red or orange.

Overall, turmeric is a natural and readily available alternative to synthetic indicators, making it a useful tool for qualitative analysis in various applications, including educational demonstrations, scientific experiments, and culinary arts.