The colour of litmus in a neutral medium is

Analysis

The question asks for the specific color of litmus paper or litmus solution when it is in a neutral medium (neither acidic nor basic).

Concept Explanation

Litmus is a water-soluble mixture of different dyes extracted from lichens. It is commonly used as an acid-base indicator in chemistry laboratories. Its color changes depending on the pH of the solution it is placed in:

• In Acidic medium: Litmus turns red.
• In Basic (alkaline) medium: Litmus turns blue.
• In Neutral medium: Litmus maintains its natural color, which is purple.

Step-by-Step Solution

1. Identify the nature of the medium: The question specifies a "neutral medium," meaning the pH is approximately 7.
2. Recall indicator properties: Litmus is unique because its original state is purple. When it reacts with hydrogen ions ($H^+$) in acids, it shifts toward red; when it reacts with hydroxide ions ($OH^-$) in bases, it shifts toward blue.
3. Determine the color: Since there is no excess of $H^+$ or $OH^-$ ions in a neutral medium to cause a shift, the litmus remains in its original, neutral color, which is purple.

Conclusion

Comparing this to the provided options:

• A. purple (Correct)
• B. pink (Usually associated with phenolphthalein in base)
• C. yellow (Associated with methyl orange in base)
• D. orange (Associated with methyl orange in neutral/acidic conditions)

Exam Tip: To remember this easily, think of the primary colors: Red (Acid) + Blue (Base) = Purple (Neutral). Keep this "color mixing" logic in mind for your chemistry practicals!