An unknown salt ' X ' on charcoal cavity test gives a white residue that turns yellow when hot and becomes white again on cooling. On treatment with dilute acid, it evolves a gas ' G &#

Question

An unknown salt ' X ' on charcoal cavity test gives a white residue that turns yellow when hot and becomes white again on cooling. On treatment with dilute acid, it evolves a gas ' G ' that turns acidified potassium dichromate paper green. Based on this information, select the correct statement.

TestHub · Accepted Answer

White residue that turns yellow when hot and white again on cooling is characterstic of ZnO , so the metal ion is $Zn^{2 +}$ .

The gas evolved turns acidified potassium dichromate paper green, indicating reduction of dichromate to $Cr^{3 +}$ , so the gas is $SO_{2} ($ not $CO_{2})$ .

Thus, the salt contains sulfite ion and is $ZnSO_{3}$ .

ZnO on heating with cobalt nitrate forms a green mass (Rinmann's green), confirming $Zn^{2 +}$ .

Chemistry - Salt Analysis Question with Solution | TestHub

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JEE Advanced (2028)