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Science · 2024 · 2 marks
CBSE 2024 · Region 2 · Set 3 · Q21
(a)Give one example of each of the following :(i)Chemical reaction showing evolution of gas.(ii)Change in the colour of the substance during a chemical reaction.OR 21. (b) Translate the following statements into chemical equations and then balance them :(i)Hydrogen sulphide gas burns in air to give water and sulphur dioxide.(ii)Silver bromide on exposure to sunlight decomposes into silver and bromine.
(a)
Give one example of each of the following :
(i)
Chemical reaction showing evolution of gas.
(ii)
Change in the colour of the substance during a chemical reaction.
OR 21. (b) Translate the following statements into chemical equations and then balance them :
(i)
Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(ii)
Silver bromide on exposure to sunlight decomposes into silver and bromine.
Marking-scheme solution
(i)
Chemical equations showing evolution of gas :
\[\mathrm{Zn}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{ZnSO}_{4}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})
\]
(ii)
Change in colour of substance during a chemical reaction
\[2 \mathrm{Cu}(\mathrm{~s})+\mathrm{O}_{2}(\mathrm{~s}) \xrightarrow{\text { Heat }} 2 \mathrm{CuO}(\mathrm{~s})
\]
(reddish-brown) (black)
(i)
\(\displaystyle 2 \mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})+3 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{SO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\)
(ii)
\(\displaystyle 2 \mathrm{AgBr}(s) \xrightarrow{\text { sunlight }} 2 \mathrm{Ag}(s)+\mathrm{Br}_{2}(g)\)
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.