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Science · 2025 · 5 marks
CBSE 2025 · Region 3 · Set 1 · Q34
(a) (i) Consider the following metals: K, Ca, Al, Cu, Ag, Fe Select from the above metals, a metal which I. does not react with oxygen even at high…
(i)
Consider the following metals : K, Ca, Al, Cu, Ag, Fe Select from the above metals, a metal which I. does not react with oxygen even at high temperature. II. reacts with oxygen at ordinary temperature and forms a protective oxide layer which prevents the metal from further oxidation. III. catches fire when kept in the open. IV. does not burn in oxygen but the hot metal is coated with a black coloured oxide layer.
(ii)
What are amphoteric oxides ? With the help of balanced chemical equations show that aluminium oxide is an amphoteric oxide.
(iii)
What are alkalis ? Give one example.
(i)
With the help of balanced chemical equations state the process of extracting (I) mercury from its ore called cinnabar, and (II) copper from its sulphide ore.
(ii)
Silver and copper articles slowly lose their shiny surfaces when exposed to air. Name the compounds formed on
(I)
silver articles, and (II) copper articles in the form of coating.
Marking-scheme solution
(a) (i) (I) Ag,
(II) Al,
(III) K,
(IV) Cu
\[\begin{aligned}
& \mathrm{Al}_{2} \mathrm{O}_{3}+6 \mathrm{HCl} \longrightarrow 2 \mathrm{AlCl}_{3}+3 \mathrm{H}_{2} \mathrm{O} \\
& \mathrm{Al}_{2} \mathrm{O}_{3}+2 \mathrm{NaOH} \longrightarrow 2 \mathrm{NaAlO}_{2}+\mathrm{H}_{2} \mathrm{O}
\end{aligned}
\]
(b)(i)
(cinnabar)
\[2 \mathrm{HgO}(\mathrm{~s}) \xrightarrow{\text { Heat }} 2 \mathrm{Hg}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})
\] (II) \(\displaystyle 2 \mathrm{Cu}_{2} \mathrm{O}+\mathrm{Cu}_{2} \mathrm{~S} \xrightarrow{\text { Heat }} 6 \mathrm{Cu}(\mathrm{s})+\mathrm{SO}_{2}(\mathrm{~g})\)
(ii)
\[\text { (I) Silver sulphide } / \mathrm{Ag}_{2} \mathrm{~S}
\] (II) Basic Copper carbonate/ \(\displaystyle \mathrm{Cu}(\mathrm{OH})_{2} . \mathrm{CuCO}_{3}\)
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CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.