In the given nuclear reaction, identify P, Q, R and S in sequence.
\( \mathrm{P} + {}^{235}_{92}\mathrm{U} \rightarrow \mathrm{Q} \rightarrow \mathrm{R} + {}^{89}_{36}\mathrm{Kr} + \mathrm{S} \)
(A) \( {}^{236}_{92}U \)
(B) \( {}^{144}_{56}Ba \)
(C) 3 \( {}^{1}_{0}n \)
(D) \( {}^{1}_{0}n \)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (D), (A), (B), (C)
This is the neutron-induced fission of uranium-235. A slow neutron is absorbed to form an unstable compound nucleus, which splits into two fragments and releases more neutrons. In every step the mass number and the atomic number are conserved.
P — the particle that starts fission: (D) a neutron, \( {}^{1}_{0}\mathrm{n} \).
Q — the compound nucleus: mass number 1 + 235 = 236, atomic number 0 + 92 = 92, that is (A) \( {}^{236}_{92}\mathrm{U} \).
R — the partner fragment of krypton: atomic number 92 − 36 = 56, which is barium, (B) \( {}^{144}_{56}\mathrm{Ba} \).
S — the neutrons released: mass number left over 236 − 144 − 89 = 3, with atomic number 0, that is (C) \( 3\,{}^{1}_{0}\mathrm{n} \).
\( \displaystyle {}^{1}_{0}\mathrm{n} + {}^{235}_{92}\mathrm{U} \rightarrow {}^{236}_{92}\mathrm{U} \rightarrow {}^{144}_{56}\mathrm{Ba} + {}^{89}_{36}\mathrm{Kr} + 3\,{}^{1}_{0}\mathrm{n} \)
Order for P, Q, R, S: (D), (A), (B), (C).
NCERT (2026-27):
Fission – “… A most important neutron-induced nuclear reaction is fission. An example of fission is when a uranium isotope \( {}^{235}_{92}\mathrm{U} \) bombarded with a neutron breaks into two intermediate mass nuclear fragments
\( \displaystyle {}^{1}_{0}\mathrm{n} + {}^{235}_{92}\mathrm{U} \rightarrow {}^{236}_{92}\mathrm{U} \rightarrow {}^{144}_{56}\mathrm{Ba} + {}^{89}_{36}\mathrm{Kr} + 3\,{}^{1}_{0}\mathrm{n} \qquad (13.10) \)”