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Fusion reaction takes place at high temperature because
A
Molecules break up at high temperature
B
Nuclei break up at high temperature
C
Atoms get ionised at high temperature
D
Kinetic energy is high enough to overcome the coulomb repulsion between nuclei
Detailed Solution
For fusion, two light nuclei must come within the range of the nuclear force (about $10^{-15}$ m).
Both nuclei are positively charged, so they repel each other; this coulomb barrier must be overcome before they can fuse.
At very high temperatures (of the order of $10^7$ to $10^9$ K), the nuclei have enough thermal kinetic energy to overcome this repulsion.
Hence fusion needs high temperature because the kinetic energy is then high enough to overcome the coulomb repulsion between nuclei.
Both nuclei are positively charged, so they repel each other; this coulomb barrier must be overcome before they can fuse.
At very high temperatures (of the order of $10^7$ to $10^9$ K), the nuclei have enough thermal kinetic energy to overcome this repulsion.
Hence fusion needs high temperature because the kinetic energy is then high enough to overcome the coulomb repulsion between nuclei.