Question

Coloured petals of some flowers indicate the presence of acid or base in a solution. An example of such flower us
(a)Hydrangea
(b)Petunia
(c)Geranium
(d)All of the above

Answer 1

Hint: Coloured petals of some flowers act as pH indicators due to the presence of oH sensitive pigments named Anthocyanin that shows a sharp difference in colours in acidic, neutral and alkaline solutions.

Complete answer:
All the flowers mentioned in the question have coloured petals that have the ability to indicate the presence of acid or base in solution. Along with these many other natural materials such as red cabbage leaves, turmeric etc can indicate the presence of acid or base in a solution. Even the popular indicator Litmus solution is also extracted from lichen which uses a plant of the division Thallophyta.

Additional Information: Most of the acid-base indicators that are commonly used are synthetic but nature has its own indicators. The three flowers mentioned in the question namely Hydrangea, petunia and Geranium have the ability to act as indicators. They give sharp colour change in different soils. Hydrangea when blooms in an acidic soil grow blue sepal colour whereas in basic or neutral soil grows red or pink sepals. In the same way, the Anthocyanin petunia results in the change of petal colours in petunia in different soils. The petals are reddish-purple and violet in acidic and basic solutions respectively. The petals of geranium show similar phenomenons due to presence of Anthocyanin pelargonin which changes from orange-red in acidic medium to blue in basic solution.
So, the correct answer is “all of the above”.

Note: All these flowers act as a pH indicator due to the presence of the water-soluble vacuolar pigment named Anthocyanin. This pigment, depending on the pH, gives different colours to these flowers or other plant parts and the colours varies from red, blue, purple to black. Due to the presence of these pigments the flowers attract pollinating agents like insects and fruits attract seed dispersal agents. These are used as natural pH indicators because they show red or pink colour in acidic solutions, in neutral solutions purple and greenish-yellow colour in alkaline solution. In a very alkaline solution, they tend to become colourless because the pigments get completely reduced.