Which number is common in isotopes?

The number of electrons,protons and neutrons in a species are equal to $18$,$16$ and $16$ respectively. Assign the proper symbol to the species.

The electronic configuration of a divalent metal ion $M^{2+}$ is $2, 8, 14$ and its atomic mass is $58 \, a.m.u.$ What is the number of neutrons in its nucleus?

Which of the following elements is isoelectronic with $Na^{+}$?

If the atomic weight of an element is $23$ times that of the lightest element and it has $11$ protons,then it contains

Isotopes of the same element have the same number of