which of these is a fusion reaction (A) ${ }^{3}{ }_{1} \mathrm{H}+{ }_{1}^{2} \mathrm{H}={ }_{2}^{4} \mathrm{He}+{ }_{0} \mathrm{n}^{1}$ (B) ${ }^{12}{ }_{7} \mathrm{C} \rightarrow{ }_{6} \mathrm{C}^{12}+\beta^{+}+\mathrm{g}$ (C) ${ }_{92} \mathrm{U}^{238} \rightarrow{ }^{206}{ }_{82} \mathrm{~Pb}+8\left({ }_{2}^{4} \mathrm{He}\right)+6\left(_{1-} \mathrm{e}\right)$ (D) None of these

Let's analyze each given reaction to determine if it is a fusion reaction. (A) \({ }^{3}{ }_{1} \mathrm{H}+{ }_{1}^{2} \mathrm{H}={ }_{2}^{4}\mathrm{He}+{ }_{0} \mathrm{n}^{1}\) Here, we have two atomic nuclei, tritium (\({ }^{3}{ }_{1} \mathrm{H}\)) and deuterium (\({ }_{1}^{2} \mathrm{H}\)), combining to form a single heavier nucleus, helium-4 (\({ }_{2}^{4}\mathrm{He}\)), and a neutron. This seems like a fusion reaction. (B) \({ }^{12}{ }_{7} \mathrm{C} \rightarrow{ }_{6}\mathrm{C}^{12}+\beta^{+}+\mathrm{g}\) In this reaction, one nucleus, carbon with a mass number of 12 and an atomic number of 7 (\({ }^{12}{ }_{7} \mathrm{C}\)), is decaying into another nucleus, carbon with a mass number of 12 and an atomic number of 6 (\({ }_{6}\mathrm{C}^{12}\)), while also emitting a positron (\(\beta^{+}\)) and a photon (g). This type of reaction is not fusion, as there's no combining of atomic nuclei. (C) \({ }_{92} \mathrm{U}^{238} \rightarrow{ }^{206}{ }_{82}\mathrm{~Pb}+8\left({ }_{2}^{4} \mathrm{He}\right)+6\left(_{1-}\mathrm{e}\right)\) In this reaction, a uranium-238 nucleus (\({ }_{92} \mathrm{U}^{238}\)) is breaking apart into a lead-206 nucleus (\({ }^{206}{ }_{82}\mathrm{~Pb}\)), eight helium-4 nuclei, and six electrons. This is a fission reaction, not fusion, as the initial nucleus is splitting into smaller ones.

Now that we analyzed each reaction, we can confidently say that the correct answer is: (A) \({ }^{3}{ }_{1} \mathrm{H}+{ }_{1}^{2} \mathrm{H}={ }_{2}^{4}\mathrm{He}+{ }_{0} \mathrm{n}^{1}\) This is a fusion reaction because two atomic nuclei, tritium and deuterium, combine to form a single heavier nucleus, helium-4, and a neutron.