Which metals follow the stock notation method?

Which one of the following elements shows both positive and negative oxidation states?

$A$ compound contains three elements $A$,$B$ and $C$. If the oxidation states are $A = +2$,$B = +5$ and $C = -2$,the possible formula of the compound is

Which of the following elements exhibits a constant valency?

Consider the elements:
$Cs, Ne, I$ and $F$
$(a)$ Identify the element that exhibits only negative oxidation state.
$(b)$ Identify the element that exhibits only positive oxidation state.
$(c)$ Identify the element that exhibits both positive and negative oxidation states.
$(d)$ Identify the element which exhibits neither the negative nor does the positive oxidation state.

Write the stock notation name of $SnO_2$.