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Science · 2026 · 4 marks
CBSE 2026 · Region 2 · Set 1 · Q28
Read the following passage and answer the questions that follow: In the given diagram, when electricity is passed through an aqueous solution of a…
Read the following passage and answer the questions that follow : In the given diagram, when electricity is passed through an aqueous solution of a common salt, a substance 'Z' is produced, along with the evolution of gases 'X' and 'Y'. When a burning matchstick is brought near the gas 'Y', it burns with a pop sound, whereas 'X' is used for disinfecting drinking water. When 'X' is passed through slaked lime, an insoluble substance 'A' is produced.
(a)
Write the names of the gases 'X' and 'Y'.
(b)
Write the balanced chemical equation for the formation of substance 'Z'.
(c)
(i)
What happens :
(I)
If a drop of red litmus solution is added to the aqueous solution of substance 'Z' ?
(II)
If $\displaystyle \mathrm{CO}_{2}$ gas is passed through ammoniacal solution of aqueous NaCl ?
OR
(ii)
Identify the substance 'A' and write the balanced chemical equation of the reaction which takes place in its preparation.
Marking-scheme solution
(a) X - Chlorine gas Y -Hydrogen gas
(b) \[2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_{2}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g})
\]
(c) (i)
(I) The red litmus solution will turn blue.
(II) Sodium hydrogen carbonate and Ammonium chloride will be formed / \(\displaystyle \mathrm{NaHCO}_{3}\) and \(\displaystyle \mathrm{NH}_{4} \mathrm{Cl}\) will be formed. /
\[\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2}+\mathrm{NH}_{3} \rightarrow \mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NaHCO}_{3}
\] (Ammonium (Sodium chloride) hydrogencarbonate)
(c) (ii)
Bleaching Powder / \(\displaystyle \mathrm{CaOCl}_{2} / \mathrm{Ca}(\mathrm{ClO})_{2}\)
\(\displaystyle \mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{Cl}_{2} \rightarrow \mathrm{CaOCl}_{2}+\mathrm{H}_{2} \mathrm{O} \quad / 2 \mathrm{Ca}(\mathrm{OH})_{2}+2 \mathrm{Cl}_{2} \rightarrow \mathrm{Ca}(\mathrm{ClO})_{2}+\mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O}\)
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CBSE Class 10 Science past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.