Question

Which is an acidic indicator?
A.Phenolphthalein
B.Methyl Orange
C.Both (A) and (B)
D.None of these

Answer 1

Hint: Consider the pH range in which a substance behaves as an acid and hence, check whether you observe a change in colour when you move to this PH range. We usually use this indicator in the laboratory to do acid base titrations.

Complete step by step answer:
An indicator is a substance which tells us whether the substance is acidic, basic or neutral in nature by changing its colour according to the solution they are put in. In the same way acidic indicators will be that indicator, which let us know whether the solution has become acidic in nature or not by changing its colour.
Talking about Phenolphthalein, it is a colourless substance which when added to water shows pink colour due to dissociation in water. So in solid state it is colourless but when in solution it changes into pink. Now when we add this acid to the solution of phenolphthalein then the pink colour starts fading and ultimately disappears. Hence it shows change in colour when the solution turns acidic. So it is an acidic indicator.
Now, coming to Methyl Orange. In solution or say in neutral water, it is yellow in colour but as soon as we make the PH of the solution acidic by adding acid, it immediately changes colour to red. It also shows change in colour and indicates the presence of acid. So, it will also be an acidic indicator.
Hence, from the above discussion, it is clear that both A and B are acidic indicators.

So, the correct option is C .

Note:
Phenolphthalein and methyl orange are the most commonly used indicators. Hence, we have to keep in mind the colour they show in acidic, basic or alkaline and neutral medium. In alkaline medium, Phenolphthalein shows pink colour and methyl orange shows yellow colour.