In the atom $_{13}Al^{27}$,the number of protons $(a)$,electrons $(b)$,and neutrons $(c)$ are present. Determine the ratio in the order $(c : b : a)$.

Calculate the number of electrons,protons,and neutrons in $Cl_{2}$,$Cl$,and $Cl^{-}$. (Given for $Cl$: $Z = 17$ and $A = 35$)

Provide the symbol,name,atomic number $(Z)$,mass number $(A)$,and the number of electrons $(e)$,protons $(p)$,and neutrons $(n)$ for elements with atomic numbers $1$ to $10$.

Match the following species with their respective number of electrons:
| Species | Number of electrons |
| :--- | :--- |
| $(a)$ $O^{2-}$ | $(i)$ $18$ |
| $(b)$ $Li^{2+}$ | (ii) $2$ |
| $(c)$ $He$ | (iii) $10$ |
| $(d)$ $Ca^{2+}$ | (iv) $1$ |

Which of the following are isoelectronic species?

Which of the following is correct?