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Chemistry · 2026 · 3 marks
CBSE 2026 · Region 2 · Set 1 · Q24
(a) Complete and balance the following equations: (i) 2 KMnO_4 → 513 K (ii) Na_2 Cr_2 O_7+2 KCl → (b) Why is it difficult to separate lanthanoid…
(a)
Complete and balance the following equations :
(i)
$\displaystyle 2 \mathrm{KMnO}_{4} \xrightarrow{513 \mathrm{~K}}$
(ii)
$\displaystyle \mathrm{Na}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+2 \mathrm{KCl} \longrightarrow$
(b)
Why is it difficult to separate lanthanoid elements in pure state ?
Marking-scheme solution
(a)(i)
2KMnO4 → K2MnO4 + MnO2 + O2
(ii)
Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl
(b)
Their separation is difficult because they have similar ionic size and similar
physical and chemical properties / Due to lanthanoid contraction.
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.