A) to obtain more aluminium
B) to decompose bauxite
C) to protect anodes
D) as a reducing agent
Correct Answer: B
Solution :
Cryolite is used in the electrolytic extraction of aluminium to decompose bauxite. \[\underset{cryolite}{\mathop{N{{a}_{3}}Al{{F}_{6}}}}\,\rightleftharpoons 3NaF+Al{{F}_{3}}\] \[Al{{F}_{3}}\rightleftharpoons A{{l}^{3+}}+3{{F}^{-}}\] At cathode \[A{{l}^{3+}}+3{{e}^{-}}\xrightarrow{{}}Al(l)\] At anode \[2A{{l}_{2}}{{O}_{3}}+12{{F}^{-}}\xrightarrow{{}}4Al{{F}_{3}}+6{{O}^{2-}}\] \[C(s)+\underset{(melt)}{\mathop{{{O}^{2-}}}}\,\xrightarrow{{}}CO(g)+2{{e}^{-}}\] \[C(s)+2\underset{(melt)}{\mathop{{{O}^{2-}}}}\,\xrightarrow{{}}C{{O}_{2}}(g)+4{{e}^{-}}\]
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