Question

Which of the following pairs are correctly matched?

• A. Isoelectronics $N^{3-},O^{2-},C{r}^{3-}$
• B. Isotones ${}_{14}S{i}^{30}{,}_{15}{p}^{31}{,}_{16}{S}^{32}$
• C. Isotopes ${}_{20}C{a}^{40}{,}_{19}{K}^{40}$
• D. Isobars ${}_8{O}^{16}{,}_8{K}^{17}{,}_8{O}^{18}$

Answer 1

Answer: (B)

Isoelectronics are those in which the total number of electrons are same.
Isotones are those in which number of neutrons are same.
Isotopes are those in which number of protons are same.
Isobars are those in which mass number is same.
(a) $\underset{\text{No. of electrons}}{}\underset{8}{N^{3-}}\underset{8}{O^{2-}}\underset{27}{C{r}^{3-}}$
So, the se are not isoelectronics
(b) $\underset{\text{No. of neutrons}}{}\underset{16}{{}_{14}S{i}^{30}}\underset{16}{{}_{15}{P}^{31}}\underset{16}{{}_{16}{S}^{32}}$
So, these are isotones.
(c) ${}_{20}C{a}^{40},{}_{19}{K}^{40}$
No. of protons are different. So, these are not isotopes.
(d) ${}_8{O}^{16},{}_8{O}^{17},{}_8{O}^{18}$
Mass number of these elements is not same. So, these are not isobars.