Question

Which of the following are isotopes?

• A. $H_1^1$, $H_1^2$, $H_1^3$
• B. $C{a}_{20}^{40}$, $A{r}_{18}^{40}$
• C. $C_6^{12}$, $C_6^{13}$, $C_6^{14}$
• D. $O_8^{15}$, $O_8^{16}$, $O_8^{17}$

Answer 1

Answer: (A), (C), (D)

The correct options are
A

$H_1^1$, $H_1^2$, $H_1^3$

C

$C_6^{12}$, $C_6^{13}$, $C_6^{14}$

D

$O_8^{15}$, $O_8^{16}$, $O_8^{17}$

$\bullet$ Isotopes have the same atomic number (same number of protons) and different mass number.

$\bullet$ Since, ${}_1^{1}H$, ${}_1^{2}H$, ${}_1^{3}H$ have the same atomic number, they are isotopes of hydrogen.

$\bullet$ Similarly, ${}_6^{12}C$, ${}_6^{13}C$, ${}_6^{14}C$ have same atomic number, hence they are isotopes of carbon.

$\bullet$ Whereas, ${}_{20}^{40}Ca$, ${}_{18}^{40}Ar$ and ${}_{26}^{58}Fe$, ${}_{27}^{58}Ni$ have different atomic numbers and hence, are not isotopes. They are isobars as they have same mass number.