Question

Why is a nuclear fusion rare?

Answer 1

Answer: If the formed nucleus of a fusion reaction has a larger binding energy than the reactants then the reaction is exothermic. Nuclear fusion is very hard to achieve. This is because it requires very rare conditions before it can proceed. Just about all natural nuclear fusion occurs in stars.

Answer 2

because it requires very rare conditions (extreme heat and lots of energy)

Step-by-step explanation:

Temperatures of approximately 150,000,000 °C (around the temp. of the sun) are required for fusion to occur on Earth therefore it is very difficult to achieve. It mostly happens in stars.