If three 4He nuclei combine to form a 12C nucleus, energy is libe

Question

If three

^{4} H e

nuclei combine to form a

^{12} C

nucleus, energy is liberated. Why can't helium nuclei combine on their own and minimize the energy?

Options:

A . He gas is rare, so collisions between nuclei are also rare;

B . It happens and the 12C we see in nature was formed by this method only in Earth's atmosphere;

C . The strong nuclear force between nucleons is attractive but short range; the Coulomb force between protons is long range, but repulsive;

D . Helium nucleus is more stable than carbon.

Answer: Option C
:
C
Nuclear interactions are interesting battle grounds of different forces - mainly the Coulomb force, which is electrostatic in nature, and the strong nuclear force.
The strong nuclear force is a strong attractive force, but only activates when you bring the nucleons closer to each other than a few femtometers. At those length scales, no force in the universe is stronger than the strong nuclear force.
The problem is,

^{4} H e

nuclei are positively charged, because of the two protons. To even bring them to a close distance, we will need to overcome the Coulomb repulsion between them, which increases as separation decreases. Only when they have reached a separation of few fermi the strong nuclear attraction becomes large enough to hold the nucleons together against the Coulomb repulsion.