Question

Which of the following is / are example (s) of isotones

A. $C_6^{13}$ and \[C_6^{12}\]
B.\[Na_{11}^{23}\] and \[Mg_{12}^{23}\]
C. \[Si_{14}^{30}\] and \[S_{16}^{32}\]
D. \[Bi_{83}^{210}\] and \[Po_{84}^{210}\]

Answer 1

Hint: We say two atoms are isotones when the number of neutrons are the same whereas the number of protons and electrons can vary.

Complete step by step answer:
Number of neutrons is calculated by subtracting the number of protons(Z) from the number of nucleons(neutrons+protons combined)(A)

A-Z=Number of neutrons

In first option:

For carbon (atomic mass 12), number of neutrons=12-6=6 and,

For carbon (atomic mass 13), the number of neutrons=13-6=7, so they aren’t isotones.

In second option:

For Na, number of neutrons=23-11=12

For Mg, the number of neutrons=23-12=11, so they won’t be isotones.

In third option:

For silicon (atomic mass 30), number of neutrons=30-14=16 and,

For sulphur (atomic mass 32), the number of neutrons=32-16=16, since the number of \[Po_{84}^{210}\]neutrons is the same, the two species are isotones.

In fourth option:

For bismuth, number of neutrons=210-83=127, and

For polonium, the number of neutrons=210-84=126, so they aren’t isotones.

So, the correct answer is “Option C”.

Note:
Isotopes are always the same elements but isobars and isotones cannot be the same elements as the number of nucleons changes. The two atoms with the same mass number but different atomic numbers are called isobars, for example $^{13}$C and $^{13}$Mg. And the atoms having the same atomic number but different mass numbers are called isotopes, for example $^{12}$C and $^{13}$C.