Which substance is commonly used as an acid-base indicator, which turns red in acidic solutions and blue in basic solutions?

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SSC CGL 2024 Tier-II Official Paper-I (Held On: 20 Jan, 2025)
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  1. Litmus paper
  2. Methyl orange
  3. Phenol
  4. Bromothymol blue

Answer (Detailed Solution Below)

Option 1 : Litmus paper
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SSC CGL Tier 1 2025 Full Test - 01
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Detailed Solution

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The correct answer is Litmus paper.

Key Points

  • Litmus paper is a common acid-base indicator used in laboratories.
  • It turns red in acidic solutions (pH less than 7).
  • It turns blue in basic solutions (pH greater than 7).
  • Litmus paper is derived from lichens, which are symbiotic associations between fungi and algae.

Additional Information

  • Acid-Base Indicators
    • Substances that change color based on the pH level of the solution they are in.
    • Common indicators include methyl orange, phenolphthalein, and bromothymol blue.
    • Each indicator has a specific pH range over which it changes color.
  • pH Scale
    • A scale ranging from 0 to 14 used to measure how acidic or basic a solution is.
    • A pH of 7 is neutral, below 7 is acidic, and above 7 is basic.
  • Lichens
    • Organisms formed from a symbiotic relationship between fungi and algae.
    • They are capable of surviving in harsh environments and are used to produce litmus.
  • Uses of Litmus Paper
    • Commonly used in educational laboratories to teach about acids and bases.
    • Used for testing the acidity or alkalinity of various substances in industrial applications.

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