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The pair that does NOT require calcination is -

1. Fe 2 O 3 and CaCO 3 ⋅ MgCO 3
2. ZnCO 3 and CaO
3. ZnO and Fe 2 O 3 ⋅ xH 2 O
4. ZnO and MgO

Correct answer: ZnO and MgO

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