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Chemistry · 2026 · 2 marks
CBSE 2026 · Region 3 · Set 1 · Q19
Explain why, on addition of 1 mol of KCl to 1 litre of water, the boiling point of water increases, while the addition of 1 mol of methyl alcohol to…
Explain why, on addition of $\displaystyle 1$ mol of KCl to $\displaystyle 1$ litre of water, the boiling point of water increases, while the addition of $\displaystyle 1$ mol of methyl alcohol to $\displaystyle 1$ litre of water decreases the boiling point. []
Marking-scheme solution
Because KCl undergoes dissociation in water to give more particles mean higher
b.p. Whereas methyl alcohol forms hydrogen bond with H2O disrupting water-
water H-bonding and lowering the b.p.
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.