The number of electrons in a neutral atom of an element is equal to its

Which of the following is not isoelectronic with $O^{2-}$?

The species that is isotonic with $_1^3T$ is .....

Which of the following has an isotopic number (neutron number) equal to that in $_{13}^{27}Al$?

What are the isotopes of chlorine? How do they differ from each other?

If the electronic configuration of a metal ion $M^{2+}$ is $2, 8, 14$ and its atomic mass is $56 \, a.m.u.$,then the number of neutrons in its nucleus is .....