Question

Which of the following are not stable?
(i) ${}_6^{14}C$
(ii) ${}_6^{13}C$
(iii) ${}_7^{14}N$
(iv) ${}_{11}^{24}Na$

• A. (i) ${}_6^{14}C$, (ii) ${}_6^{13}C$, (iv) ${}_{11}^{24}Na$
• B. (i) ${}_6^{14}C$, (ii) ${}_6^{13}C$, (iii) ${}_7^{14}N$
• C. (i) ${}_6^{14}C$, (iii) ${}_7^{14}N$, (iv) ${}_{11}^{24}Na$
• D. None of these

Answer 1

The correct option is A (i) ${}_6^{14}C$, (ii) ${}_6^{13}C$, (iv) ${}_{11}^{24}Na$

An unstable isotope undergoes radioactive decay meaning it looses energy over time while emitting radiation.

Carbon-14 atoms have two extra neutrons, giving them a total of 8 neutrons. Carbon-14 has an atomic mass of 14 ( = 6 protons + 8 neutrons). The extra neutrons make the nucleus of carbon-14 unstable.

C-13 is relatively stable than C-12 but not as stable as C-12.

Also Na-24 is unstable and undergoes radioactive decay giving Mg.