Which of the following species does not have the same number of electrons as the other three species?

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) $1$ |

Find the number of neutrons,electrons,and protons in the following species:
$(i)$ $_{15}^{31}P$
$(ii)$ $_{11}^{23}Na^{+}$
$(iii)$ $_{16}^{32}S^{2-}$
$(iv)$ $_{101}^{235}X$
$(v)$ $_{20}^{40}Ca^{2+}$
$(vi)$ $_9^{19}F^{-}$

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

If the number of neutrons in $_{8}O^{16}$ is doubled and the number of electrons is halved,what is the percentage change in its mass?

On comparing the chemical reactivity of $C^{12}$ and $C^{14}$,it is revealed that: