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Science · 2026 · 5 marks
CBSE 2026 · Region 5 · Set 1 · Q29
Attempt either option (A) or (B): (A) (i) Give reasons for the following: (I) Ionic compound have generally high melting points and boiling points.…
Attempt either option (A) or (B) :
(i)
Give reasons for the following :
(I)
Ionic compound have generally high melting points and boiling points.
(II)
Solder, an alloy of lead and tin, is used for welding electrical wires.
(III)
Carbon cannot reduce the oxides of Na or Mg.
(ii)
The reaction of compound 'X' with aluminium is used to join railway tracks :
(I)
Identify the compound 'X'.
(II)
Name the reaction.
(III)
Write the balanced chemical equation of the reaction of compound 'X' with aluminium.
(i)
Write the balanced chemical equations when :
(I)
A mixture of $\displaystyle \mathrm{Cu}_{2} \mathrm{O}$ and $\displaystyle \mathrm{Cu}_{2} \mathrm{~S}$ is heated.
(II)
ZnS is heated in the presence of oxygen.
(ii)
Give reasons for the following :
(I)
The wires carrying current in homes have a coating of PVC.
(II)
To make hot water tanks, copper is used and not steel.
(iii)
Show the formation of ionic compound CaO with electron dot structure. [Atomic number : $\displaystyle \mathrm{Ca}=20, \mathrm{O}=8$ ]
Marking-scheme solution
(a)
In optically rarer medium speed of light is more and in optically denser medium speed of light is less.
(b) \(\displaystyle \mathrm{A}<\mathrm{C}<\mathrm{B}\)
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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.