Addition of two neutrons in an atom $A$ would

Compared with an atom of atomic weight $12$ and atomic number $6$,the atom of atomic weight $13$ and atomic number $6$:

Identify the isoelectronic pair from the following.

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) $1$ |

Two atoms have the same atomic mass but different atomic numbers. Such atoms are called as:

Fluoride ion $(F^-)$ is isoelectronic with: