Give the symbol of the following species:
$(i)$ Number of electrons,protons,and neutrons are $10, 8$,and $8$ respectively.
$(ii)$ $Ca$ $(Z = 20)$ and nucleon number $= 40$.
$(iii)$ Species with mass number $25$,protons $12$ (magnesium),and electrons $10$.
$(iv)$ Species of Bromine in which $(Z = 35)$,electrons $36$,and neutrons $45$.
$(v)$ $+2$ positive and $-2$ negative ions that are isoelectronic with $Al^{3+}$ $(Z = 13)$.

(N/A) $(i)$ The species has $8$ protons,so it is Oxygen $(O)$. With $10$ electrons and $8$ protons,it is $O^{2-}$. Mass number $= 8 + 8 = 16$. Symbol: ${ }_{8}^{16} O^{2-}$.
$(ii)$ Calcium $(Ca)$ with $Z = 20$ and mass number $40$. Symbol: ${ }_{20}^{40} Ca$.
$(iii)$ Magnesium $(Mg)$ with $Z = 12$,mass number $25$,and $10$ electrons. Symbol: ${ }_{12}^{25} Mg^{2+}$.
$(iv)$ Bromine $(Br)$ with $Z = 35$,$36$ electrons,and $45$ neutrons. Mass number $= 35 + 45 = 80$. Symbol: ${ }_{35}^{80} Br^{-}$.
$(v)$ $Al^{3+}$ has $13 - 3 = 10$ electrons. $A$ $+2$ ion with $10$ electrons must have $12$ protons $(Mg^{2+})$. $A$ $-2$ ion with $10$ electrons must have $8$ protons $(O^{2-})$. Symbols: ${ }_{12}^{25} Mg^{2+}$ and ${ }_{8}^{16} O^{2-}$.