Atomic number means

The electronic configuration of a dipositive ion $M^{2+}$ is $2, 8, 14$ and its atomic mass is $56$. The number of neutrons in the nucleus would be :

The number of protons,electrons and neutrons in a species are equal to $17$,$18$ and $18$ respectively. Which of the following will be the proper symbol of this species?

Which of the following is an isotonic pair?

The ratio of the number of neutrons in $_6C^{12}$ and $_{14}Si^{28}$ is ....

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) $1$ |