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

The nitrogen atom has $7$ protons and $7$ electrons. The nitride ion $(N^{3-})$ will have:

The number of protons,neutrons and electrons in the ion ${ }_{16}^{32} S^{2-}$ respectively are

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) $1$ |

An atom has a mass number of $25$ and contains $13$ neutrons in its nucleus. What is the charge of its ion if it forms a stable octet?

Which number is common in isotopes?