Question

The triad of the nuclei that is isotonic is:
A. ${}_6{{\text{N}}^{14}}{\text{, }}{}_7{{\text{N}}^{14}}{\text{, }}{}_9{{\text{F}}^{19}}$
B. ${}_6{{\text{C}}^{14}}{\text{, }}{}_7{{\text{N}}^{15}}{\text{, }}{}_9{{\text{F}}^{17}}$
C. ${}_6{{\text{C}}^{14}}{\text{, }}{}_7{{\text{N}}^{14}}{\text{, }}{}_9{{\text{F}}^{17}}$
D. ${}_6{{\text{C}}^{12}}{\text{, }}{}_7{{\text{N}}^{14}}{\text{, }}{}_9{{\text{F}}^{19}}$

Answer 1

Hint: Isotones are referred to the atoms having the same number of neutrons. Neutrons are the neutral particles. Due to different mass number and atomic number, they show different chemical properties. They are different from isotopes and isobars.

Complete step by step solution:
Protons are the positively charged particles. Neutrons have no electric charge. It is found inside the nucleus. While electrons are the negatively charged particles found outside the nucleus of an atom, in the electron levels. Each orbit or level can hold a maximum of electrons. Electrons are involved in the formation of chemical bonds.
Isotone is a group of nuclides that has the same number of neutrons, but the number of protons is different. Thus its mass number will be different since mass number is the sum of neutrons and protons.
Now we have to find the isotonic nuclides. So let’s consider the options. Element is expressed with respect to atomic number, ${\text{Z}}$ and mass number, ${\text{A}}$, as ${}_{\text{Z}}{{\text{E}}^{\text{A}}}$.
A. In ${}_6{{\text{N}}^{14}}{\text{,}}$ it has ${\text{Z = 6}}$ and ${\text{A = 14}}$, i.e. it has $6$ protons and $8$ neutrons. In ${}_7{{\text{N}}^{14}}{\text{,}}$ it has $7$ protons and $7$ neutrons. In ${}_9{{\text{F}}^{19}},$ it has $9$ protons and $10$ neutrons. So these are not isotones since one differs in the number of neutrons.
B. In ${}_6{{\text{C}}^{14}}{\text{,}}$ it has $6$ protons and $8$ neutrons. In ${}_7{{\text{N}}^{15}}{\text{,}}$ it has $7$ protons and $8$ neutrons. In ${}_9{{\text{F}}^{17}},$ it has $9$ protons and $8$ neutrons. Thus three nuclides have $8$ neutrons. So they are said to be isotones.
C. In ${}_6{{\text{C}}^{14}}{\text{,}}$ it has $6$ protons and $8$ neutrons. In ${}_7{{\text{N}}^{14}}{\text{,}}$ it has $7$ protons and $7$ neutrons. In ${}_9{{\text{F}}^{17}},$ it has $9$ protons and $8$ neutrons. Thus, not isotones.
D. In ${}_6{{\text{C}}^{12}}{\text{,}}$ it has $6$ protons and $6$neutrons. In ${}_7{{\text{N}}^{14}}{\text{,}}$ it has $7$ protons and $7$ neutrons. In ${}_9{{\text{F}}^{19}},$ it has $9$ protons and $10$ neutrons. Thus not isotones.

Hence the correct option is B.

Note: Total number of neutrons can be calculated by subtracting atomic number from the mass number since mass number is the sum of protons and neutrons and atomic number is the number of protons.
i.e. total number of neutrons${\text{n}} = {\text{A}} - {\text{Z}}$