A solution turns blue litmus red but the same substance in dry form has no effect on litmus. What is the most appropriate reason?
Answer and explanation
Correct answer: Dry substance has no water for ion formation
Acidic behaviour in aqueous solution depends on the formation of hydrogen or hydronium ions. Water allows an acid to ionise or dissociate, and these ions change blue litmus to red. In the dry state, ions are not freely available to move and interact with the indicator, so the colour change may not occur. Thus A gives the appropriate reason. The other choices contradict the definition and use of acid–base indicators.
Frequently asked questions
What is the correct answer to this question?
Dry substance has no water for ion formation
Why is this the correct answer?
Acidic behaviour in aqueous solution depends on the formation of hydrogen or hydronium ions. Water allows an acid to ionise or dissociate, and these ions change blue litmus to red. In the dry state, ions are not freely available to move and interact with the indicator, so the colour change may not occur. Thus A gives the appropriate reason. The other choices contradict the definition and use of acid–base indicators.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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