A brown substance X on heating in air forms a substance Y

A brown substance X on heating in air forms a substance Y. When hydrogen gas is passed over heated Y, it again changes back into X. Name the substance X and Y.

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The substance X is copper. On heating in air, it forms copper oxide Y.

When hydrogen gas is passed over black copper oxide then it turns brown as oxygen is removed by hydrogen.

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From which book this question is taken?

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