An atom has $28$ neutrons and $21$ clectrons. If it is a cation with a $+3$ charge, what is its correct symbol?

$($a$){28}^{58}N{i}^{3+}$

b$.{24}^{32}C{r}^{3+}$

$($c$){?}_{21}^{28}S{e}^{3+}$

$($d$){?}_{21}^{49}S{e}^{3+}$

Which of the following is not a name of a cation?

a$)$Phosphide

$($b$)$ Cobalt$($II$)$

$($c$)$ Potassium

$($d$)$ Ammonium

$12\mathrm{.}0-$gram sample of $C{r}_2(S{O}_4{)}_3$ contains how many sulfur atoms?

$($a$)5\mathrm{.}53{10}^{21}$

$($b$)1\mathrm{.}84{10}^{21}$

$($c$)5\mathrm{.}53{10}^{22}$

$($d$)6\mathrm{.}67{10}^{22}$