Identify the isoelectronic pair from the following.

In the neutral state,the element $M$ consists of the isotopes $_{14}M^{28}$,$_{14}M^{29}$,and $_{14}M^{30}$ in the ratio $60 : 30 : 20$ respectively. Correct statements about $M$ in the natural state include that:

Which of the following is not a hydrogen-like species?

Give the symbol of the following species:
$(i)$ Number of electrons,protons,and neutrons are $10, 8$,and $8$ respectively.
$(ii)$ $Ca$ $(Z = 20)$ and nucleon number $= 40$.
$(iii)$ Species with mass number $25$,protons $12$ (magnesium),and electrons $10$.
$(iv)$ Species of Bromine in which $(Z = 35)$,electrons $36$,and neutrons $45$.
$(v)$ $+2$ positive and $-2$ negative ions that are isoelectronic with $Al^{3+}$ $(Z = 13)$.

Substances which have identical chemical properties but differ in atomic weights are called

Which of the following pairs represents isobars?