Question

An indicator prepared from red cabbage changes its colour in strongly alkaline solution to:
[A] Green
[B] Orange
[C] Blue
[D] None of these

Answer 1

Hint: Red cabbage contains a chemical compound known as anthocyanin. It is the compound responsible for its colour. It also changes its colour depending upon the acidity of the solution. Red cabbage is naturally dark red or purple in colour.

Complete step by step solution:
Before answering this question, let us understand what an indicator is and how the indicator given to us i.e. red cabbage works.
We know that in chemistry, we use indicators for the determination of the pH of a solution. Different indicators work differently in acidic, basic and neutral solutions.
Here, red cabbage indicator is given to us. We might use red cabbage as an indicator because it contains a natural pH indicator which is responsible for change in colour depending on the acidity of the solution.
The red cabbage is red in colour due to the presence of a chemical known as flavin which is an anthocyanin. Anthocyanin is a water soluble pigment and is found in black grapes, blueberries, raspberry and many others that are red, black, blue or purple in colour.
In neutral solution, it is purple in colour. In acidic and alkaline solutions it is red and greenish-yellow respectively.
We can understand from the above discussion that the red cabbage indicator turns greenish yellow in alkaline solutions.

Therefore, the correct answer is option [A] green.

Note: In chemistry we use indicators during titration to mark the end point of a titration. We see that in acid-base titrations, generally the end is marked by the change in colour of the solution. Depending upon the titration, it is very important for us to choose suitable indicators which will indicate the equivalence point.