CBSE 2025 · Region 6 · Set 1 · Q32 · 5 marks

(a)

(i)OR(b)

Account for the following :

(I)

Orange colour of $\displaystyle \mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}$ ion changes to yellow when treated with an alkali.

(II)

Zn, Cd and Hg are non-transition elements.

(III)

$\displaystyle \mathrm{E}^{\circ}$ value for $\displaystyle \mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ couple is highly positive $\displaystyle (+1 \cdot 57 \mathrm{~V})$ as compared to $\displaystyle \mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}$.

(ii)

What happens when :

(I)

Manganate ion undergoes disproportionation reaction in acidic medium ?

(II)

$\displaystyle \mathrm{KMnO}_{4}$ is heated ?

CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.