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JEE Main levelSingle correct optionDifficulty 2 of 3mt122

In the Baeyer process, bauxite is digested with concentrated $NaOH$ at about $500 K$ under pressure. The undissolved residue (red mud) is mainly

A $Al (OH) X_{3}$
B $Fe X_{2} O X_{3}$
C $Na [Al (OH) X_{4}]$
D $Na X_{3} AlF X_{6}$

Answer: B

Alumina dissolves as

Na [Al (OH) X_{4}]

while the basic impurity ferric oxide stays undissolved and is filtered off as red mud.

Na X_{3} AlF X_{6}

is not present in bauxite; it is the cell electrolyte.

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