Question

what is released through nuclear fusion in stars?
energy
gas
mass
pressure

Explanation:

Nuclear fusion in stars combines light nuclei (like hydrogen) to form heavier ones (like helium). According to Einstein's mass - energy equivalence ($E = mc^{2}$), a small amount of mass is converted into a large amount of energy during this process. Gas is the medium for fusion, mass is the "input" that gets converted (not released as mass), and pressure is related to the conditions in stars but not what's released by fusion.

Answer:

energy