What is the oxidation number of $N$ in $HNO_4$?

The oxidation number of $Fe$ and $S$ in iron pyrites are

$A$ compound contains atoms of $x, y$ and $z$ elements. Oxidation numbers of $x, y$ and $z$ are $+3, +5$ and $-2$ respectively. Identify the possible formula of this compound?

State whether the following statements are True or False:
$(1)$ The oxidation number of nitrogen in ammonium chloride $(NH_4Cl)$ is $(-3)$.
$(2)$ The oxidation number of $C$ in methyl chloride $(CH_3Cl)$ is $(-2)$.
$(3)$ In the following reaction,the oxidation number of $Br$ changes from $0$ to $+5$: $Br_2 \to BrO_3^-$.

The oxidation number of $C$ in $C_6H_{12}O_6$ is:

One mole of $N_2H_4$ loses $10 \ moles$ of electrons to form a new compound $Z$. Assuming that all the nitrogen atoms appear in the new compound, what is the oxidation state of nitrogen in $Z$? (There is no change in the oxidation state of hydrogen.)