Why can the strength of sodium hydroxide decrease when it is left exposed to air?
Answer and explanation
Correct answer: It reacts with carbon dioxide in the air
The governing concept is the reaction of a strong base with an acidic oxide. Sodium hydroxide absorbs carbon dioxide from air and can form sodium carbonate, for example: 2NaOH + CO₂ → Na₂CO₃ + H₂O. This consumes some NaOH, so less active base remains and its measured strength may decrease. Option A is correct; the other choices describe impossible or irrelevant changes.
Frequently asked questions
What is the correct answer to this question?
It reacts with carbon dioxide in the air
Why is this the correct answer?
The governing concept is the reaction of a strong base with an acidic oxide. Sodium hydroxide absorbs carbon dioxide from air and can form sodium carbonate, for example: 2NaOH + CO₂ → Na₂CO₃ + H₂O. This consumes some NaOH, so less active base remains and its measured strength may decrease. Option A is correct; the other choices describe impossible or irrelevant changes.
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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