Match List I with List II
| LIST I | LIST II | ||
|---|---|---|---|
| A. | \( {}^{222}_{86}\mathrm{Rn}\rightarrow{}^{218}_{84}\mathrm{Po} \) | I. | \( \beta^{+} \) particle |
| B. | \( {}^{214}_{83}\mathrm{Bi}\rightarrow{}^{214}_{84}\mathrm{Po} \) | II. | \( \beta^{-} \) particle |
| C. | \( {}^{234}_{90}\mathrm{Th}\rightarrow{}^{234}_{92}\mathrm{U} \) | III. | \( \alpha \) particle |
| D. | \( {}^{22}_{11}\mathrm{Na}\rightarrow{}^{22}_{10}\mathrm{Ne} \) | IV. | \( 2\beta^{-} \) particle |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-II, C-IV, D-I
Compare the mass number A and the atomic number Z before and after each decay. An alpha particle removes 4 from A and 2 from Z. A beta decay leaves A unchanged and changes Z by one unit: \( \beta^{-} \) raises Z by 1, \( \beta^{+} \) lowers Z by 1.
(A) \( {}^{222}_{86}\mathrm{Rn}\rightarrow{}^{218}_{84}\mathrm{Po} \) — this matches (III) \( \alpha \) particle. A falls by 4 (222 to 218) and Z falls by 2 (86 to 84).
(B) \( {}^{214}_{83}\mathrm{Bi}\rightarrow{}^{214}_{84}\mathrm{Po} \) — this matches (II) \( \beta^{-} \) particle. A is unchanged and Z rises by 1.
(C) \( {}^{234}_{90}\mathrm{Th}\rightarrow{}^{234}_{92}\mathrm{U} \) — this matches (IV) \( 2\beta^{-} \) particle. A is unchanged and Z rises by 2, which needs two \( \beta^{-} \) decays in succession.
(D) \( {}^{22}_{11}\mathrm{Na}\rightarrow{}^{22}_{10}\mathrm{Ne} \) — this matches (I) \( \beta^{+} \) particle. A is unchanged and Z falls by 1 (11 to 10).
Note: It seems that there is a mistake in the original NTA paper, which prints the product in item D as \( {}^{22}_{10}\mathrm{Na} \) (sodium) when it should read \( {}^{22}_{10}\mathrm{Ne} \) (neon), since the element with atomic number 10 is neon. In item C the paper prints uranium correctly with atomic number 92.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Alpha Decay – “… In this process, it is observed that since 42He contains two protons and two neutrons, the mass number and the atomic number of the daughter nucleus decreases by four and two, respectively.”
Beta Decay – “… In beta minus (β–) decay, an electron is emitted by the nucleus, as in the decay of 3215P … In beta plus (β+) decay, a positron is emitted by the nucleus, as in the decay of 2211Na
\( \displaystyle {}^{22}_{11}\mathrm{Na} \rightarrow {}^{22}_{10}\mathrm{Ne} + e^{+} + \nu \qquad (13.23) \)”