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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…
(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 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.