The electronegativity of aluminium is similar to

$Be$ and $Al$ exhibit many properties which are similar, but the two elements differ in :

Aluminum dissolves in mineral acids and aqueous alkalis and thus shows amphoteric character. A piece of aluminum foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning match stick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated nitric acid, reaction doesn't proceed. Explain the reason. 

Which one of the following is the correct statement ?

During metallurgy of aluminium bauxite is dissolved in cryolite because

The purification of alumina is called