CBSE 2025 · Region 7 · Set 3 · Q33 · 5 marks

(i)

Account for the following :

(I)

The $\displaystyle \mathrm{E}_{\mathrm{Mn}^{2+} / \mathrm{Mn}}^{\circ}$ value for manganese is highly negative, whereas $\displaystyle \mathrm{E}_{\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}}^{\circ}$ is highly positive.

(II)

Actinoids show wide range of oxidation states.

(III)

Transition metals have high melting points.

(ii)

Complete the following ionic equations :

(I)

$\displaystyle 5 \mathrm{SO}_{3}{ }^{2-}+2 \mathrm{MnO}_{4}{ }^{-}+6 \mathrm{H}^{+} \longrightarrow$

(II)

$\displaystyle 2 \mathrm{MnO}_{4}{ }^{-}+\mathrm{H}_{2} \mathrm{O}+\mathrm{I}^{-} \longrightarrow$

(II)

OR(b) Answer the following questions :

(i)

Name two elements of 3d series for which the third ionisation enthalpies are quite high.

(ii)

Out of $\displaystyle \mathrm{KMnO}_{4}$ and $\displaystyle \mathrm{K}_{2} \mathrm{MnO}_{4}$, which one is paramagnetic and why ?

(iii)

Write any one consequence of lanthanoid contraction.

(iv)

How do you prepare potassium manganate from pyrolusite ore ?

(v)

Why is the ability of oxygen more than fluorine to stabilise higher oxidation states of transition metals ?

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.