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Select the ore in which the metal has oxidation state +2 AND which produces carbon dioxide gas on calcination.

1. Galena
2. Fools gold
3. Siderite
4. Malachite

Correct answer: Malachite

Solution

Malachite [Cu2(OH)2CO3] contains copper in the +2 state and, upon calcination, decomposes to give CuO, CO2, and H2O. This satisfies both conditions. Siderite (FeCO3) also satisfies but Malachite is the expected answer in this context.

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