In the electrolytic refining of metals, the insoluble impurities present in the impure metal settle down at the bottom of the container below the anode. What is this called?

Which method is used to collect $H_2$ gas in a gas jar in the laboratory?

What is the number of electrons lost by a metal atom to form a positive ion called?

Which non-metal element is used in the vulcanization of rubber?

$A, B$ and $C$ are three elements which undergo chemical reactions according to the following equations:
$A_{2}O_{3} + 2B \rightarrow B_{2}O_{3} + 2A$
$3CSO_{4} + 2B \rightarrow B_{2}(SO_{4})_{3} + 3C$
$3CO + 2A \rightarrow A_{2}O_{3} + 3C$
$(a)$ Which element is the most reactive?
$(b)$ Which element is the least reactive?
$(c)$ What is the type of reactions listed above?

Why is iron galvanised with zinc? Can it be galvanised with copper? If not,why?