Nuclear fusion is not used as a source of enegy because

Analyze the question: The question asks why nuclear fusion is not widely used as a practical energy source, even though the Sun and stars run on it.

Concept: Fusion is the joining of two light nuclei (e.g., deuterium and tritium, isotopes of hydrogen) to form a heavier nucleus, releasing a large amount of energy.

Every nucleus carries a positive charge, so two nuclei repel each other strongly (Coulomb repulsion). To force them close enough to fuse, they must move at enormous speeds. That requires extremely high temperatures, on the order of millions of degrees Celsius (about 100 million °C for the reactions we want on Earth). Building and containing such conditions is the main technological barrier.

Checking each option:

• A. Very high temperature is needed for the reaction. This is correct. It is the central practical obstacle: we have no easy way to reach and sustain these temperatures and contain the hot plasma.
• B. The fuel is not easy to obtain. Incorrect. Deuterium is abundant in seawater.
• C. Less energy is released. Incorrect. Fusion releases more energy per unit mass of fuel than fission.
• D. The reaction is too slow. Incorrect. Once conditions are met, fusion reactions happen very fast (as in a hydrogen bomb).

Answer: Option A.

Tip: Remember "Fission = easy to start, Fusion = hard to start." Fusion needs extreme heat to overcome the repulsion between positive nuclei. If a WASSCE or JAMB question asks about the difficulty of fusion, think "high temperature."