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The d & f Block Elements — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryThe d & f Block Elements2 Marks
Question
(A) why are transition elements good catalysts ?
(B) Zinc does not exhibit variable oxidate state, why?
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Answer

(A) Transition elements and their compounds are effective catalysts due to:
- Variable Oxidation States: They can change oxidation states to form unstable intermediate complexes with reactants.
- Large Surface Area: They provide a platform for reactants to be adsorbed, increasing the local concentration and lowering the activation energy.
(B) Zinc ( $Z=30$ ) has a ground state electronic configuration of $[A r] 3 d^{10} 4 s^2$. It does not show variable oxidation states because:
- Completely Filled $d$-subshell: The $3 d^{10}$ configuration is highly stable.
- Involvement of only s-electrons: Only the two electrons from the $4 s$ orbital are lost to form the $Z n^{2+}$ ion. The stable $3 d^{10}$ electrons do not participate in bonding under normal conditions.

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