Question

The iso neutronic triad of nuclei is
A.$_6{C^{14}}$, $_7{N^{14}}$, $_9{F^{17}}$
B.$_6{C^{14}}$, $_7{N^{14}}$, $_9{F^{19}}$
C.$_6{C^{14}}$, $_7{N^{15}}$, $_9{F^{17}}$
D.$_6{C^{12}}$, $_7{N^{14}}$, $_9{F^{19}}$

Answer 1

Recall the concept of iso neutronic triads. Check what numbers are given with the symbol of the elements in the options. Use the formula for the determination of the number of neutrons in terms of atomic mass number and atomic number. Calculate the number of neutrons in each group of elements given in the options.

Complete step by step answer:
The iso neutronic triad of nuclei is the group of three elements having the same number of neutrons in their nuclei.
An element with its atomic number and atomic mass number represented in the form $_z{E^A}$, where $E$ is the symbol of the element, $z$ is the atomic number of the element and $A$ is the atomic mass number of the element.
The number of neutrons $n$ in the nucleus of an element $_z{E^A}$ can be calculated by subtracting the atomic number of elements from its atomic mass number.
$n = A - z$
For element $_6{C^{14}}$, the atomic number is 6 and atomic mass number is 14. Hence, the number of neutrons are $n = 14 - 6 = 8$.
For element$_7{N^{14}}$, the atomic number is 7 and atomic mass number is 14. Hence, the number of neutrons are $n = 14 - 7 = 7$.
For element $_9{F^{17}}$, the atomic number is 9 and atomic mass number is 17. Hence, the number of neutrons are $n = 17 - 9 = 8$.
For element $_9{F^{19}}$, the atomic number is 9 and atomic mass number is 19. Hence, the number of neutrons are $n = 19 - 9 = 10$.
For element $_7{N^{15}}$, the atomic number is 7 and atomic mass number is 15. Hence, the number of neutrons are $n = 15 - 7 = 8$.
For element $_6{C^{12}}$, the atomic number is 6 and atomic mass number is 12. Hence, the number of neutrons are $n = 12 - 6 = 6$.
The above calculations show that the group of elements given in options A, B and D do not have the same number of neutrons.
Hence, the options A, B and D are incorrect.

From the above calculations of the number of neutrons in different elements, it can be concluded that the elements $_6{C^{14}}$, $_7{N^{15}}$ and $_9{F^{17}}$ has the same number of neutrons.
This group of elements is given in option C only.

So, the correct answer is option (C).

Note:
The student may get confused with which number given with the symbol of the element is the atomic number and which number is the atomic mass number of the element. The students should always keep in mind that the number at the base of the symbol of element is atomic number and at the top of symbol is atomic mass number. One can also remind in a way that the larger number is mass number and smaller number is atomic number.