Question

An isotone of ${}_{36}^{86}Kr$ is _________.

• A. ${}_{19}^{39}K$
• B. ${}_{35}^{80}Br$
• C. ${}_{40}^{90}Zr$
• D. ${}_{50}^{119}Sn$

Answer 1

The correct option is C ${}_{40}^{90}Zr$

Isotones are species that have the same number of neutrons but different number of protons.
Number of neutrons = mass number – atomic number
Number of neutrons in ${}_{36}^{86}Kr=86–36=50$
Number of neutrons in ${}_{19}^{39}K=39–19=20$
Number of neutrons in ${}_{35}^{80}Br=80–35=45$
Number of neutrons in ${}_{40}^{90}Zr=90–40=50$
Number of neutrons in ${}_{50}^{119}Sn=119–50=69$

Therefore, ${}_{40}^{90}Zr$ is an isotone of ${}_{36}^{86}Kr$.