Identify the letter of the choice that best completes the statement or answers the question.

What is the oxidation number of $P$ in $P{O}_3^{3-}?$

a$.-6$

b$.-3$

c$.+3$

d$.+6$

e$.+5$

In which substance does sulfur have the lowest oxidation number?

a$.H_{2}S{O}_4$

b$.H_{2}S$

c$.S{O}_3^{2-}$

d$.H_2{S}_2{O}_3$

e$.$ elemental sulfur

What is the oxidation number of chlorine in perchloric acid, $HCl{O}_4?$

a$.+1$

b$.+3$

c$.+5$

d$.+7$

e$.-1$

How many electrons need to be added to balance the following half$-$reaction?

$B{r}_{2(g)}2B{r}^{-}(aq)$

a$.$ one electron to the right side

b$.$ one electron to the left side

c$.$ two electrons to the left side

d$.$ two electrons to the right side

e$.$ no electrons are needed for this equation

$5.$ How does the oxidation number of $Bi$ change when $Bi{O}_3^{-}$reacts to form $Bi(OH{)}_3?$

a$.$ decreases by $3$

b$.$ decreases by $2$

c$.$ increases by $4$

d$.$ no change

e$.$ increase by $1$

$6.$ How many electrons need to be added to balance the following half$-$reaction?

$C{u}^{2+}(aq)C{u}_{(s)}$

a$.$ one electron to the right side

b$.$ one electron to the left side

c$.$ two electrons to the right side

d$.$ two electrons to the left side

e$.$ no electrons are needed for this equation