An isotone of $_{32}Ge^{76}$ is:
$(i) \, _{32}Ge^{77}$
$(ii) \, _{33}As^{77}$
$(iii) \, _{34}Se^{77}$
$(iv) \, _{34}Se^{78}$

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) $1$ |

The pair,in which ions are isoelectronic with $Al^{3+}$ is ..... .

What is the number of electrons in a neutral atom that has $20$ protons in its nucleus?

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 :

Which one of the following sets of ions represents a collection of isoelectronic species? (Given: Atomic Number: $F: 9, Cl: 17, Na: 11, Mg: 12, Al: 13, K: 19, Ca: 20, Sc: 21$)