Question

Which colour will be acquired by an aqueous solution of ammonium hydroxide when a few drops of phenolphthalein indicator are added to it?

• A. Yellow
• B. Orange
• C. Red
• D. Pink

Answer 1

The correct option is D

Pink

1. Phenolphthalein is an organic dye. In neutral or acidic solution, it is colourless while in the basic solution, the colour of the indicator changes to pink.
2. Ammonium hydroxide $\left({\mathrm{NH}}_4\mathrm{OH}\right)$ is a weak base.
3. The solution of ammonium hydroxide contains two ions $({{\mathrm{NH}}_4}^{+}\mathrm{and}{\mathrm{OH}}^{-})$ and anything that has hydroxide ions in an aqueous solution is considered the base in nature.
4. The pH of ammonium hydroxide lies between 7 to 10.
5. Due to the basic nature of ammonium hydroxide solution, the colour of the solution becomes pink when a few drops of phenolphthalein indicator are added to it.
6. Therefore, the pink colour is acquired by an aqueous solution of ammonium hydroxide when a few drops of phenolphthalein indicator are added to it.

Hence, option (D) is correct.