Question

An element is represented by ${}_Z{X}^A$, where Z is atomic number which is also equal to number of proton, A is mass number and X is symbol of the element.
Mass number (A) = Number of protons (Z) + Number of neutrons.
Isoelectronic: Species/ elements having same number of electron
Isodiaphers: Elements having same value of $|(A-2Z)|$
Isotopes: Atoms having same number of proton

Which of the following is a pair of isodiaphers?

• A. ${}_{19}^{39}Kand{}_9^{19}F$
• B. ${}_6^{13}Cand{}_7^{14}N$
• C. ${}_{92}^{238}Uand{}_{90}^{231}Th$
• D. ${}_{52}^{130}Teand{}_{54}^{130}Xe$

Answer 1

The correct option is A ${}_{19}^{39}Kand{}_9^{19}F$

Isodiaphers are species that have different atomic and mass numbers, but have the same number of neutrons in excess i.e.the difference between the number of protons and the number of neutrons in the nucleus is same.
$\begin{array}{ccccc}\text{Option No.}& \text{Elements}& \text{Number of neutrons}& \text{Number of protons}& \text{Difference between number of protons and neutrons}\\ \left(a\right)& {}_{19}^{39}K& 39-19=20& 19& 1\\ & {}_9^{19}F& 19-9=10& 9& 1\\ \left(b\right)& {}_6^{13}C& 13-6=7& 6& 1\\ & {}_7^{14}N& 14-7=7& 7& 0\\ \left(c\right)& {}_{92}^{238}U& 238-92=146& 92& 54\\ & {}_{90}^{231}Th& 231-90=141& 90& 51\\ \left(d\right)& {}_{52}^{130}Te& 130-52=78& 52& 26\\ & {}_{54}^{130}Xe& 130-54=76& 54& 22\end{array}$