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Which of the following dye is colourless at acidic pH and becomes red at basic pH?

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in Fermentation Technology by (72.1k points)
Which of the following dye is colourless at acidic pH and becomes red at basic pH?

(a) Methyl red

(b) Thymol blue

(c) Phenolphthalein

(d) Phenol red

The question was posed to me in an online interview.

Origin of the question is Isolation and Screening of Industrially Important Microbes topic in division The Isolation, Preservation and Improvement of Industrial Microorganisms of Fermentation Technology

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Best answer
Correct option is (c) Phenolphthalein

Explanation: Phenolphthalein has a pH range between 8.0 – 10.0. It is colourless at pH 8.0 and becomes red at pH above 10.0. It belongs to the phthalein family that is employed as an acid-base indicator.

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