Question

Which of the following options is/are correct regarding the colour of phenolphthalein and methyl orange in acidic and basic medium?

• A. Phenolphthalein:
  Colour in acidic solution: Colourless
  Colour in basic solution: Pink
• B. Methyl orange:
  Colour in acidic solution: Yellow
  Colour in basic solution: Red
• C. Phenolphthalein:
  Colour in acidic solution: Pink
  Colour in basic solution: Colourless
• D. Methyl orange:
  Colour in acidic solution: Red
  Colour in basic solution: Yellow

Answer 1

Answer: (A), (D)

Methyl orange:
Colour in acidic solution: Red
Colour in basic solution: Yellow

Theory :
Titration : pH indicator is an auxiliary substance added for physical detection of completion of a titration at its equivalence point. It generally shows colour change on the completion of the titration.
Indicators : Indicators are substances which indicate the end-point of a titration by changing their colour.
Indicators are either weak organic acids or weak organic bases having characteristically different colours in ionised and unionised forms.

Phenolphthalein and Methyl orange both show distinct colours in acidic and basic solutions.

$\text{Indicator}\text{color change(acidic to basic solution)}\text{Methyl Orange}\left(\text{colorless to pink}\right)\text{Phenolphthalein}\left(\text{Red to Yellow}\right)\text{Phenol Red}\left(\text{Yellow to Red )}\text{Bromothymol}\right(\text{Orange to Blue})$