$^{235}_{92}U + ^1_0n → ^{145}_{56}Ba + ^{88}_{36}Kr + 3^1_0n + Energy$ The equation above represent a/an

Analyze the question: We have a heavy nucleus (uranium-235) hit by a neutron. It splits into two smaller nuclei (barium-145 and krypton-88), releases 3 neutrons, and gives off energy. We need to name this type of process.

Concept:

• Nuclear fission: a heavy nucleus splits into two (or more) lighter nuclei, usually after absorbing a neutron, releasing a large amount of energy and extra neutrons.
• Nuclear fusion: two light nuclei join to form a heavier nucleus (e.g. hydrogen isotopes forming helium, as in the sun).
• Alpha emission: a nucleus ejects a helium nucleus, ⁴₂He.
• Endothermic reaction: absorbs energy. Here energy is released, so the reaction is exothermic.
• Thermal dissociation: a compound breaks down reversibly on heating. This is a chemical process, not a nuclear one.

Check the balance:

• Mass numbers: left = 235 + 1 = 236. Right = 145 + 88 + 3(1) = 236 ✔
• Atomic numbers: left = 92 + 0 = 92. Right = 56 + 36 + 0 = 92 ✔

The equation is balanced, so it is a valid nuclear equation.

Interpretation:

• A neutron strikes a heavy nucleus (U-235).
• The nucleus splits into two medium-sized nuclei (Ba and Kr).
• 3 neutrons are released, which can go on to split more uranium atoms in a chain reaction.
• Energy is released.

All of these are the hallmarks of nuclear fission, which is the principle behind nuclear reactors and atomic bombs.

Answer: C. Nuclear fission

Exam tip: Remember it this way: fission = split (a big nucleus splits into smaller ones), while fusion = fuse (small nuclei join). If you see a neutron hitting a heavy atom like uranium or plutonium and producing two medium-sized atoms, think fission.