Understanding Indicator Colour Changes in Acids and Bases

Indicators are special substances used in chemistry to detect whether a solution is acidic or basic. They work by changing their colour when exposed to different pH levels. Each indicator has a specific colour change range.

Key Indicators and Their Characteristic Colour Shifts

The question involves four common indicators. Let's recall their typical behaviour in acidic and basic environments:

• Turmeric: This natural indicator is yellow in acidic conditions and turns a distinct reddish brown when it comes into contact with a base. In acids, it shows no colour change from its original yellow.
• China rose (Hibiscus): The petals of the china rose flower provide an indicator that is typically dark pink or red in acidic solutions. In basic solutions, it changes to green.
• Phenolphthalein: This synthetic indicator is widely used. It remains colourless in acidic solutions but exhibits a vibrant pink colour in basic (alkaline) solutions.
• Methyl orange: Methyl orange is another common synthetic indicator. In acidic solutions, it typically appears pink or red. In basic solutions, it changes to yellow.

Analysing the Question's Table and Identifying Variables

The problem presents a table showing indicator behaviour, with some values denoted by letters A, B, C, and D. We need to determine what these letters represent.

The question asks for the values of A, B, C, and D respectively. Let's break down what each letter signifies based on the table structure:

Step-by-Step Determination of A, B, C, and D

1. Finding A:

   In the table, 'A' is the colour change for Turmeric in bases. Based on its known properties, Turmeric turns reddish brown in basic solutions.

2. Finding B:

   'B' indicates the colour change for China rose in bases. The standard colour change for China rose in basic solutions is green.

3. Finding C:

   'C' represents the colour change for Phenolphthalein in acids. Phenolphthalein is known to be colourless in acidic environments.

4. Finding D:

   'D' corresponds to the colour change for Methyl orange in acids. While methyl orange is typically pink/red in acids, the provided options suggest 'orange' for this value. We will consider 'orange' as the intended answer for D.

Conclusion: The Sequence of Colour Changes

Combining the determined values for A, B, C, and D in order, we get the sequence:

• A = Reddish brown
• B = Green
• C = Colourless
• D = Orange

Thus, the correct sequence representing A, B, C, D respectively is reddish brown, green, colourless, orange.