Question:
Which of the following indicators does not show any color in an acidic solution?
Which of the following indicators does not show any color in an acidic solution?
Show Hint
Phenolphthalein is colorless in acid and pink/magenta in base. It is used as a titration indicator when titrating a strong acid with a strong base. The endpoint is the first permanent pink color. In contrast, methyl orange is red in acid and yellow in base — it is used when titrating a weak base with a strong acid.
Updated On: Jun 10, 2026
- Methyl orange
- Methylene blue
- Phenolphthalein
- Blue litmus
Show Solution
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The Correct Option is C
Solution and Explanation
Concept:
Chemical indicators are substances that change color depending on whether the medium is acidic, basic, or neutral. Different indicators have different color behaviors in acidic and basic conditions. Some indicators are colorless in acidic solutions and become colored in basic solutions, while others do the reverse.
Step 1: Recall the behavior of each indicator in acidic solutions.
(A) Methyl Orange in Acid:
Methyl orange is a pH indicator that turns
red in acidic solution (pH $<$ 3.1). It is orange at intermediate pH and yellow in alkaline conditions. Therefore, methyl orange clearly shows a distinct color (red) in acidic solution. So option (A) is
not the answer.
(B) Methylene Blue in Acid:
Methylene blue is primarily a redox indicator and a biological stain. It is blue in its oxidized form. It does show color (remains blue or slightly changes) in acidic solutions. Therefore, it shows color in acidic medium. Option (B) is
not the answer.
(C) Phenolphthalein in Acid:
Phenolphthalein is one of the most commonly used acid-base indicators. Its key property is:
• In
acidic and neutral solutions (pH $<$ 8.2): phenolphthalein is
colorless (no color).
• In
basic solutions (pH $>$ 8.2): phenolphthalein turns
pink/magenta.
Therefore, in acidic solution, phenolphthalein shows
no color at all. This perfectly matches the question. Option (C) is
the correct answer.
(D) Blue Litmus in Acid:
Blue litmus paper turns
red in acidic solution. This is one of the most fundamental acid-base tests taught in school. So blue litmus clearly shows a color change (blue to red) in acidic medium. Option (D) is
not the answer.
Step 2: Summary table of indicators in acid.
tabular|l|l|
Indicator &
Color in Acidic Solution
Methyl orange & Red
Methylene blue & Blue (retains color)
Phenolphthalein &
Colorless (no color)
Blue litmus & Red
tabular
Chemical indicators are substances that change color depending on whether the medium is acidic, basic, or neutral. Different indicators have different color behaviors in acidic and basic conditions. Some indicators are colorless in acidic solutions and become colored in basic solutions, while others do the reverse.
Step 1: Recall the behavior of each indicator in acidic solutions.
(A) Methyl Orange in Acid:
Methyl orange is a pH indicator that turns
red in acidic solution (pH $<$ 3.1). It is orange at intermediate pH and yellow in alkaline conditions. Therefore, methyl orange clearly shows a distinct color (red) in acidic solution. So option (A) is
not the answer.
(B) Methylene Blue in Acid:
Methylene blue is primarily a redox indicator and a biological stain. It is blue in its oxidized form. It does show color (remains blue or slightly changes) in acidic solutions. Therefore, it shows color in acidic medium. Option (B) is
not the answer.
(C) Phenolphthalein in Acid:
Phenolphthalein is one of the most commonly used acid-base indicators. Its key property is:
• In
acidic and neutral solutions (pH $<$ 8.2): phenolphthalein is
colorless (no color).
• In
basic solutions (pH $>$ 8.2): phenolphthalein turns
pink/magenta.
Therefore, in acidic solution, phenolphthalein shows
no color at all. This perfectly matches the question. Option (C) is
the correct answer.
(D) Blue Litmus in Acid:
Blue litmus paper turns
red in acidic solution. This is one of the most fundamental acid-base tests taught in school. So blue litmus clearly shows a color change (blue to red) in acidic medium. Option (D) is
not the answer.
Step 2: Summary table of indicators in acid.
tabular|l|l|
Indicator &
Color in Acidic Solution
Methyl orange & Red
Methylene blue & Blue (retains color)
Phenolphthalein &
Colorless (no color)
Blue litmus & Red
tabular
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