Isotopes were discovered by

Match the following species with the correct number of electrons present in them:

Species	Number of Electrons
$(i) Be^{2+}$	$(a) 0$
$(ii) H^{+}$	$(b) 10$
$(iii) Na^{+}$	$(c) 2$
$(iv) Mg^{+}$	$(d) 11$

Among the following,the set of isoelectronic ions is:

Elements $A$ and $B$ have the same mass number. Their atomic numbers are $27$ and $30$ respectively. If the mass number of $A$ is $57$,find the number of neutrons in $B$.

The expression $Ze$ gives :

Which one of the following is not an iso-electronic pair?