Question

{"given":"Four nuclear reactions are given. Identify which are fusion reactions.\n$$\\text{Fusion: lighter nuclei combine} \\Rightarrow \\text{heavier nucleus}$$\n$$\\text{Conservation laws: } A_{\\text{left}} = A_{\\text{right}},\\quad Z_{\\text{left}} = Z_{\\text{right}}$$","key_observation":"In nuclear fusion, two or more lighter nuclei combine to form a comparatively heavier nucleus, with both mass number $A$ and atomic number $Z$ conserved. Fission involves a heavy nucleus splitting into lighter fragments.","option_analysis":[{"label":"(A)","text":"$_{6}^{13}\\mathrm{C} + _{1}^{1}\\mathrm{H} \\rightarrow _{6}^{14}\\mathrm{C} + 4.3$ MeV","verdict":"incorrect","explanation":"Mass number: $13+1=14$ ✓. Atomic number: left $= 6+1 = 7$, right $= 6$ ✗. Atomic number is NOT conserved, making this reaction physically impossible altogether."},{"label":"(B)","text":"$_{6}^{12}\\mathrm{C} + _{1}^{1}\\mathrm{H} \\rightarrow _{7}^{13}\\mathrm{N} + 2$ MeV","verdict":"correct","explanation":"Mass number: $12+1=13$ ✓. Atomic number: $6+1=7$ ✓. Two lighter nuclei (C and H) combine to form a heavier nucleus (N) — this is a valid fusion reaction."},{"label":"(C)","text":"$_{7}^{14}\\mathrm{N} + _{1}^{1}\\mathrm{H} \\rightarrow _{8}^{15}\\mathrm{O} + 7.3$ MeV","verdict":"correct","explanation":"Mass number: $14+1=15$ ✓. Atomic number: $7+1=8$ ✓. Two lighter nuclei (N and H) combine to form a heavier nucleus (O) — this is a valid fusion reaction."},{"label":"(D)","text":"$_{92}^{235}\\mathrm{U} + _{0}^{1}n \\rightarrow _{54}^{140}\\mathrm{Xe} + _{36}^{94}\\mathrm{Kr} + 2\\,_{0}^{1}n + \\gamma + 200$ MeV","verdict":"incorrect","explanation":"A heavy nucleus $^{235}\\mathrm{U}$ splits into lighter nuclei ($\\mathrm{Xe}$ and $\\mathrm{Kr}$) — this is nuclear fission, not fusion. Also note: $Z=36$ corresponds to Krypton (Kr), not Strontium."}],"answer":"(B) and (C)","formula_steps":[]}