What is the molecular formula of cryolite?

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

Which acid is formed when sulfur dioxide reacts with water?

Of the three metals $X, Y$ and $Z$,$X$ reacts with cold water,$Y$ with hot water,and $Z$ with steam only. Identify $X, Y$ and $Z$ and also arrange them in the order of increasing reactivity.

$A, B$ 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?

Explain the following:
$(a)$ The reactivity of $Al$ decreases if it is dipped in $HNO_3$.
$(b)$ Carbon cannot reduce the oxides of $Na$ or $Mg$.