Introduction:
An indicator is a substance that is used to detect the presence of a chemical substance. It is widely used in various scientific experiments and analytical techniques. Indicators work by undergoing a physical or chemical change when they come into contact with the target substance. One of the most common ways an indicator shows the presence of a chemical substance is by changing color.
Explanation:
Indicators are used in various fields, including chemistry, biology, and environmental science, to determine the presence or absence of specific substances. Here, we will discuss in detail how indicators work and why changing color is the most common way they indicate the presence of a chemical substance.
Working of an Indicator:
When an indicator is exposed to a specific chemical substance, it undergoes a change in its physical or chemical properties. This change can be observed and used to determine the presence or absence of the target substance. The change can occur due to various factors such as pH, temperature, or the formation of a complex between the indicator and the target substance.
Why changing color is a common indicator:
The most common way an indicator shows the presence of a chemical substance is by changing its color. This is because:
1. Selectivity: Indicators are designed to be selective towards specific substances. They react only with the target substance and undergo a change in color, making it easier to identify the presence of that particular substance.
2. Visual Observation: Color change is easily visible to the naked eye. It provides a clear and immediate indication of the presence of the target substance without the need for complex instruments or equipment.
3. Sensitivity: Indicators can exhibit different shades or intensities of color change depending on the concentration of the target substance. This allows for the detection of even small amounts of the substance.
4. Versatility: Indicators can be used in various forms such as solutions, paper strips, or solid powders. This makes them adaptable to different experimental setups and analytical techniques.
Conclusion:
Indicators are crucial tools in chemical analysis and scientific research. Their ability to change color in the presence of specific substances makes them highly effective in detecting and identifying the presence of chemicals. By understanding the principles behind indicator reactions, scientists can leverage their properties to conduct accurate and reliable experiments.

Understanding Indicators
Indicators are substances that help identify the presence of a particular chemical by undergoing a noticeable change. The most common type of indicator is one that changes color, making option 'B' the correct answer.
How Indicators Work
- Indicators react with specific chemicals in a solution.
- This reaction often leads to a visual change, typically in color.
- For example, litmus paper changes from blue to red in acidic solutions and from red to blue in basic solutions.
Types of Indicators
- pH Indicators: These change color at different pH levels, providing information about the acidity or basicity of a solution.
- Universal Indicators: These show a range of colors corresponding to various pH levels, giving a more precise understanding of the solution's nature.
- Phenolphthalein: This indicator is colorless in acidic solutions but turns pink in basic solutions.
Importance of Color Change
- The color change is a quick and easy method to determine the chemical nature of a substance.
- It allows chemists and students to visually assess chemical reactions without complex instruments.
Conclusion
In summary, indicators are essential tools in chemistry used primarily for their ability to change color in response to different chemical environments. This characteristic not only aids in experiments but also enhances our understanding of chemical properties in a simple, visual manner.