Explanation

(d)
Ostwald process: It is used to manufacture $HNO_{3}$.
Hoope’s process It is the method used to purify aluminium. Pure Al makes anode and impure aluminium makes cathode in this reaction.
Hall’s process It is used to purify bauxite having no specific impurity.
Baeyer’s process It is used to purify bauxite having chief impurity of iron.
$\ \ \ \ \ \ \ \ \ \ \therefore$ Hoope’s process is correct answer.