What is the name of the apparatus used for the electrolysis of pure water?

What is the chemical formula of bauxite?

Explain the following statements:
$(a)$ Most metal oxides are insoluble in water but some of these dissolve in water. What are these oxides and their solutions in water called?
$(b)$ At ordinary temperature,the surfaces of metals such as magnesium,aluminium,and zinc are covered with a thin layer. What is the composition of this layer? State its importance.
$(c)$ Some alkali metals can be cut with a knife.

Which of the following is a mineral of sulfur?

Which kind of impurities are present in the ores? What are these impurities collectively known as?

What are the substances added to a catalyst to increase its efficiency called?