Question

Which of the following is/are the correct statement(s) above a universal indicator.
(A) It is a mixture of some indicators.
(B) It shows the change in colour at different pH with altogether different colours for a change in pH by $1$ units.
(C) Phenolphthalein is a universal indicator.
(D) A mixture of methyl red, $\alpha $-naphthol, phthalein blue shows different colours
between pH range $4$ to $11$

Answer 1

Hint: As we know that universal indicator is a kind of pH indicator which is made up of various compounds and is used to indicate the acidity and basicity of a solution. It can be a paper form like a strip which changes colour or present in the solution form.

Complete Step by step answer:The Universal indicator is also a pH indicator and mainly composed of water, $1 - $propanol, phenolphthalein, sodium salt, $NaOH$, methyl red, thymol blue and bromothymol blue monosodium salt. So we can say that it is a mixture of some indicators. When the pH range is less than $3$, it shows red colour and indicates the medium as acidic, when the pH is between $3$ to $6$ it becomes orange or yellow showing a weak acid. When the colour is green, pH is $7$ and medium is neutral, when medium is weakly basic then it shows blue colour and the pH range is $8$ to $11$ and when the pH is above $11$, it represents the medium as a strong alkali and the colour shown is violet or indigo. Hence it shows the change in colour at different pH with altogether different colours for a change in pH by $1$ units and a mixture of methyl red, $\alpha $-naphthol, phthalein blue shows different colours between pH range $4$ to $11$ is also correct.
Phenolphthalein is an organic compound belonging to the family phthalein which is an acid-base indicator. Below pH $8.5$, it is colourless and when the pH is above $9.0$it shows a pink to deep red colour change. It is also a universal indicator.

Thus, all the given options are correct.

Note: A universal indicator can be present in paper form where a strip of coloured paper is given which changes the colour according to the medium it is dipped in and the solution form as a mixture of components discussed above.