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Science · 2026 · 3 marks
CBSE 2026 · Region 4 · Set 3 · Q27
Answer the following : $\displaystyle \mathbf{3} \times \mathbf{1}=\mathbf{3}$(a)Write two observations when green coloured crystals of ferrous sulphate are heated in a boiling tube.(b)Why brown coloured copper powder turns black on heating ?(c)What happens when limestone is heated strongly ?
Answer the following : $\displaystyle \mathbf{3} \times \mathbf{1}=\mathbf{3}$
(a)
Write two observations when green coloured crystals of ferrous sulphate are heated in a boiling tube.
(b)
Why brown coloured copper powder turns black on heating ?
(c)
What happens when limestone is heated strongly ?
Marking-scheme solution
(a)
Green colour of the crystal changes brown.
Colourless gases with odour of burning sulphur.
(b)
Copper changes to copper (II) oxide which is black in colour./
\[\underset{\text { Brown }}{\mathbf{2 C u}(\mathbf{s})}+\mathbf{O}_{\mathbf{2}}(\mathbf{g}) \xrightarrow{\text { Heat }} \underset{\substack{\text { Copper(II) Oxide } \\ \text { (Black) }}}{\mathbf{2 C u O}(\mathbf{s})}
\]
(c)
Calcium oxide (quick lime) and colourless gas \(\displaystyle \left(\mathrm{CO}_{2}\right)\) is evolved) /
\[\mathrm{CaCO}_{4}(\mathrm{~s}) \xrightarrow{\text { Heal }} \mathrm{CaO}[\mathrm{~s})+\mathrm{CO}_{2}(\mathrm{~g})
\]
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CBSE Class 10 Science past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.