Chemistry S and P - Block Elements (S - Block Elements Not In Syllabus ) JEE ADVANCED Previous Year Question Subjective Type
Published on: August 14, 2026

A white solid is either Na 2 O or Na 2 O 2 . A piece of red litmus paper turns white when it is dipped into a freshly made aqueous solution of the white solid.

(i) Identify the substances and explain with balanced equation.

(ii) Explain what would happen to the red litmus if the white solid were the other compound.

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(i) Na 2 O 2 is powerful oxidant and bleaching agent and bleaches red litmus paper to white in aqueous solution according to the following reaction,

Na 2 O 2 + 2H 2 O ⎯→ 2NaOH + H 2 O + [O]

[O] + Litmus ⎯→ White (bleaching)

(ii) The other compound Na 2 O will give NaOH on dissolution in water according to the following reaction.

Na 2 O + H 2 O ⎯→ 2NaOH.

The red litmus will turn to blue due to stronger alkaline nature of NaOH

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