Q.What is an isotone? Give an example.

Nuclei of different elements, or different forms of the same element, can be compared and classified along three distinct axes, depending on which of $Z$ (atomic number), $A$ (mass number) or $N$ (neutron number) they happen to share:

Isotopes share the same atomic number $Z$ but differ in mass number $A$ - the same element, but with different numbers of neutrons. Hydrogen provides the classic example: $^{1}_{1}H$ (ordinary hydrogen, 0 neutrons), $^{2}_{1}H$ (deuterium, 1 neutron) and $^{3}_{1}H$ (tritium, 2 neutrons) are all isotopes of hydrogen, each with exactly one proton. Since chemical behaviour is governed by the number of electrons (equal to $Z$), every isotope of a given element shares essentially identical chemical properties and occupies the very same single position in the periodic table, regardless of how many neutrons it carries; only the isotope's mass (and, for unstable isotopes, its nuclear stability) differs. Carbon's four naturally occurring isotopes ($^{11}C$, $^{12}C$, $^{13}C$, $^{14}C$) illustrate how unevenly isotopes can be distributed in nature - about 98.9% of natural carbon is $^{12}C$, only 1.1% is $^{13}C$, and a mere $0.0001\%$ is the radioactive isotope $^{14}C$ used in carbon dating. …