(C) In the industrial Bayer process, the sodium aluminate solution is cooled and seeded with freshly precipitated aluminium hydroxide $(Al(OH)_3)$. Th

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Both $(A)$ and $(B)$ are practised

(C) In the industrial Bayer process, the sodium aluminate solution is cooled and seeded with freshly precipitated aluminium hydroxide $(Al(OH)_3)$. This seeding induces the precipitation of $Al(OH)_3$ from the supersaturated solution. Additionally, carbon dioxide $(CO_2)$ is often bubbled through the solution to neutralize the excess sodium hydroxide, which further promotes the precipitation of aluminium hydroxide. Therefore, both methods are commonly practised in industrial settings.

Class 12 Chemistry General Principles and Processes of Isolation of Elements Mix Examples of General Principles and processes of Isolation of Elements

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In aluminium extraction by the Bayer process, alumina is extracted from bauxite by sodium hydroxide at high temperature and pressure: $Al_2O_{3(s)} + 2 OH^-_{(aq)} + 3 H_2O_{(l)} \rightarrow 2 [Al(OH)_4]^-_{(aq)}$. Solid impurities such as $Fe_2O_3$ and $SiO_2$ are removed and then $[Al(OH)_4]^-$ is reprecipitated: $2 [Al(OH)_4]^-_{(aq)} \rightarrow Al_2O_3 \cdot 3 H_2O_{(s)} + 2 OH^-_{(aq)}$. In the industrial world:

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A
Carbon dioxide is added to precipitate the alumina
B
Temperature and pressure are dropped and the supersaturated solution is seeded
C
Both $(A)$ and $(B)$ are practised
D
The water is evaporated