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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3qa126

Blue crystals of $CuSO X_{4} \cdot 5 H X_{2} O$ are heated first gently and then to a bright red heat. Select all correct statements.

AGentle heating gives a white anhydrous solid, which turns blue again when a few drops of water are added.
BAt a bright red heat the residue becomes black $CuO$ with evolution of sulphur oxides.
CThe final residue is red $Cu X_{2} O$ because copper(II) is reduced to copper(I).
DThe oxidation state of copper is +2 in the hydrate, the anhydrous salt and the black residue.

Answer: A, B, D

CuSO X_{4} \cdot 5 H X_{2} O CuSO X_{4} + 5 H X_{2} O

(reversible on adding water) and then

CuSO X_{4} CuO + SO X_{3}

(partly decomposing further). Copper stays +2 throughout, and the residue is black

CuO

, not

Cu X_{2} O

. The first three statements are correct.

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