Methyl orange is red and phenolphthalein is colourless in a solution. Which substance is suitable to neutralise it?
Answer and explanation
Correct answer: Sodium hydroxide solution
Methyl orange is red in a strongly acidic medium, while phenolphthalein remains colourless in acidic and neutral solutions. Together these observations indicate that the unknown solution is acidic. Neutralisation requires an alkali to supply hydroxide ions that react with hydrogen ions to form water. Sodium hydroxide is therefore suitable, making option A correct. Vinegar, lemon juice, and dilute acid would add more acid rather than neutralise it.
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What is the correct answer to this question?
Sodium hydroxide solution
Why is this the correct answer?
Methyl orange is red in a strongly acidic medium, while phenolphthalein remains colourless in acidic and neutral solutions. Together these observations indicate that the unknown solution is acidic. Neutralisation requires an alkali to supply hydroxide ions that react with hydrogen ions to form water. Sodium hydroxide is therefore suitable, making option A correct. Vinegar, lemon juice, and dilute acid would add more acid rather than neutralise it.
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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