Energy is continuously generated in the Sun mainly due to which of the following processes occurring in its core?

Introduction / Context:
The Sun is the primary source of energy for life on Earth, and understanding how it produces this enormous amount of energy is a key concept in astrophysics and general science. This question asks you to identify the main physical process responsible for the Sun's continuous energy generation deep inside its core.

Given Data / Assumptions:

• The Sun is a star composed mainly of hydrogen and helium.
• The core of the Sun has extremely high temperature and pressure.
• Energy is produced continuously over billions of years.
• We must choose between nuclear fusion, nuclear fission, natural radioactivity and artificial radioactivity.

Concept / Approach:
Nuclear fusion is the process in which light atomic nuclei combine to form heavier nuclei, releasing large amounts of energy in the process. In the Sun's core, hydrogen nuclei (protons) fuse through a multi-step sequence known as the proton–proton chain to form helium. Nuclear fission, in contrast, is the splitting of heavy nuclei such as uranium, which is used in many nuclear power plants on Earth but is not the dominant process in the Sun. Radioactivity describes spontaneous decay of unstable nuclei and is not the main energy source in normal stars. Therefore, nuclear fusion is the correct answer.

Step-by-Step Solution:
Step 1: Recall that the Sun consists mainly of hydrogen gas, especially in its core. Step 2: Under the extreme pressure and temperature in the core, hydrogen nuclei are forced close enough to overcome electrostatic repulsion. Step 3: These hydrogen nuclei fuse in a series of reactions (proton–proton chain) to form helium, with some mass converted into energy according to E = m * c^2. Step 4: The huge energy released in each fusion reaction sustains the Sun's bright radiation over billions of years. Step 5: Recognise that this is nuclear fusion, not fission or simple radioactivity, and select fusion as the correct process.

Verification / Alternative check:
Astrophysical models and observations of solar neutrinos strongly support the nuclear fusion model for energy production in the Sun. The proton–proton chain, along with other fusion cycles like the CNO cycle in more massive stars, explains the observed luminosity and lifetime of stars. Nuclear fission, on the other hand, would consume heavy nuclei and is not consistent with the Sun's composition. Natural radioactivity does occur in some cosmic environments but cannot account for the enormous and sustained energy output of the Sun.

Why Other Options Are Wrong:
Nuclear fission: This process powers many nuclear reactors on Earth but is not responsible for the Sun's main energy output, because the Sun is not primarily composed of heavy fissile elements like uranium.

Radioactivity: Although some radioactive processes occur in the universe, they are not dominant in the Sun's core energy generation.
Artificial radioactivity: This is induced in laboratories and reactors on Earth and has no connection to natural processes inside the Sun.

Common Pitfalls:
Students sometimes mix up fission and fusion because both involve nuclear reactions and energy release. A helpful memory trick is: fusion “fuses” light nuclei like hydrogen into helium and is what powers stars, whereas fission “splits” heavy nuclei and is used in many human-made nuclear power plants and weapons. Remember that stars are mostly hydrogen, which naturally suggests fusion as the main energy process.

Final Answer:
Energy in the Sun is continuously generated mainly due to Nuclear fusion reactions in its core.