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Chemistry · 2026 · 3 marks
CBSE 2026 · Region 2 · Set 2 · Q24
(a) Complete and balance the following equations: 2+1 (i) 4 FeCr_2 O_4+8 Na_2 CO_3+7 O_2 → (ii) 5 Fe^2++ MnO_4^-+8 H^+ → (b) Explain why actinoid…
(a)
Complete and balance the following equations : $\displaystyle 2+1$
(i)
$\displaystyle 4 \mathrm{FeCr}_{2} \mathrm{O}_{4}+8 \mathrm{Na}_{2} \mathrm{CO}_{3}+7 \mathrm{O}_{2} \longrightarrow$
(ii)
$\displaystyle 5 \mathrm{Fe}^{2+}+\mathrm{MnO}_{4}{ }^{-}+8 \mathrm{H}^{+} \longrightarrow$
(b)
Explain why actinoid contraction is greater from element to element than lanthanoid contraction.
Marking-scheme solution
(a)(i)
4FeCr2O4 + 8Na2CO3 + 7O2 → 8Na2CrO4 + 2Fe2O3 + 8CO2
(ii)
5Fe2+ + MnO4− + 8H+ → Mn2+ + 4H2O + 5Fe3+
(b)
Because of poor shielding by 5f electrons in actinoids as compared to that of
4f electrons in the lanthanoids.
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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.