ICSE Class 10 Physics: Radioactivity — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: What is radioactivity? Who discovered it?
  Ans: Radioactivity is the spontaneous disintegration of unstable atomic nuclei with emission of radiation (alpha, beta, or gamma rays). It was discovered by Henri Becquerel in 1896 while studying uranium salts. Marie Curie and Pierre Curie further discovered radium and polonium.
• Q: Compare alpha, beta, and gamma radiation.
  Ans: Alpha (α): Helium nucleus (2p+2n), charge +2, mass 4u, least penetrating (stopped by paper), highest ionising power. Beta (β): High-speed electron, charge -1, negligible mass, moderate penetration (stopped by aluminium), moderate ionising. Gamma (γ): Electromagnetic radiation, no charge, no mass, most penetrating (stopped by thick lead), least ionising.
• Q: What is nuclear fission? Give one example.
  Ans: Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei with release of enormous energy and neutrons when bombarded by a slow neutron. Example: ²³⁵U + ¹n → ¹⁴¹Ba + ⁹²Kr + 3¹n + energy. This is the principle of nuclear power plants and atom bombs. Each fission releases about 200 MeV.

Long Answer / Application Questions (4-6 Marks)

• Q: What is nuclear fusion? Why is it difficult to achieve on Earth?
  Ans: Nuclear fusion is the combining of two light nuclei to form a heavier nucleus with release of energy. Example: 4¹H → ⁴He + 2e⁺ + energy (occurs in the Sun). It is difficult on Earth because it requires extremely high temperature (about 10⁸ K) and pressure to overcome the electrostatic repulsion between positively charged nuclei.
• Q: State two uses and two hazards of radioactivity.
  Ans: Uses: (1) Medical — radiotherapy using cobalt-60 to treat cancer. (2) Carbon dating — using C-14 to determine age of archaeological specimens. Hazards: (1) Radiation causes mutations in DNA, leading to cancer and genetic disorders. (2) Nuclear waste remains radioactive for thousands of years, posing disposal challenges.

Exam Tips for This Chapter

• Revise all definitions and laws from Radioactivity — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Radioactivity — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Radioactivity carries 8-12 marks in the board exam