Answer: The correct option is 2.
Explanation: There are two types of nuclear reactions:
1) Nuclear fission: These reactions are defined as the reactions in which a heavier unstable nuclei breaks into two or more smaller stable nuclei.
2) Nuclear fusion: These reactions are the ones where two smaller nuclei fuse together or combine together to form a larger nuclei.
In the question, we need to find the fusion reaction which forms elements heavier than helium.
Option 1: In this fusion reaction occurs but the nuclei is Helium itself.
Option 2: In this also fusion reaction occurs and the nuclei is heavier than Helium which is Neon.
![_8^{16}\textrm{O}+_2^4\textrm{He}\rightarrow _{10}^{20}\textrm{Ne}](https://tex.z-dn.net/?f=_8%5E%7B16%7D%5Ctextrm%7BO%7D%2B_2%5E4%5Ctextrm%7BHe%7D%5Crightarrow%20_%7B10%7D%5E%7B20%7D%5Ctextrm%7BNe%7D)
Option 3 and Option 4: These two reactions are nuclear fission reactions of Uranium-235 because one heavier element is breaking into more than 2 products.
Hence, the correct option is 2.