Answer:
<em>the mass of one helium nucleus should be</em> <em>less than the mass of four hydrogen nuclei.</em>
Explanation:
Deep inside the core of the Sun, enough protons can collide into each other with enough speed that they stick together to form a helium nucleus and generate a tremendous amount of energy at the same time. This process is called nuclear fusion.
The mass-to-energy conversion is described by Einstein's famous equation:
E = mc2, or, in words, energy equals mass times the square of the velocity of light. Because the velocity of light is a very large number, this equation says that lots of energy can be gained from using up a modest amount of mass.
Photons In the proton-proton chain reaction, hydrogen nuclei are converted to helium nuclei through a number of intermediates. The reactions produce high-energy photons (gamma rays) that move through the "radiative layer" surrounding the core. This layer takes up 60 percent of the radius of the Sun. It takes a million years for energy to get through this layer into the "convective layer", because the photons are constantly intercepted, absorbed and re-emitted. In the core, the helium nuclei make up 62% of the mass (the rest is still hydrogen). The radiative and convective layers have about 72% hydrogen, 26% helium, and 2% heavier elements (by mass). The energy produced by fusion is then transported to the solar surface and emitted as light or ejected as high-energy particles.
