Atoms, Radioactivity & Reactions MCQs with Answers
Solved Atoms, Radioactivity & Reactions MCQs with answers — atomic structure, isotopes, alpha/beta/gamma rays, nuclear fission, half-life & reactions. Free quiz + PDF for PPSC, FPSC, NTS, CSS & PMS.
Atoms, Radioactivity & Reactions — Master Reference for Pakistani Competitive Exams
The chapter Atoms, Radioactivity & Reactions is among the most repeated Everyday Science topics in Pakistan’s PPSC, FPSC, NTS, CSS, PMS, OTS, CTS, BPSC, KPPSC and SPSC One Paper exams. Almost every Junior Clerk, Tehsildar, Assistant, Sub-Inspector, Lecturer and BPS-14 to BPS-17 paper carries 2–4 MCQs from this chapter — and it is core CSS Screening MPT (General Science & Ability) content. This page consolidates 50 solved MCQs covering the structure of the atom (electrons, protons, neutrons), isotopes, the three pioneers (Dalton, Rutherford, Bohr), radioactive decay, half-life, alpha/beta/gamma radiation with their charges and penetration power, nuclear fission (U-235 vs U-238), the difference between an atomic bomb and a nuclear reactor, the electromagnetic spectrum with VIBGYOR/ROYGBIV, and the most-asked physical vs chemical change distinctions (rusting, condensation, hydrogenation, photosynthesis, combustion). For wider context, see Wikipedia: Radioactive Decay and the official IAEA: Nuclear Fission reference.
The Three Types of Radiation — Quick Reference
| Radiation | Charge | Nature | Penetration | Stopped by |
|---|---|---|---|---|
| Alpha (α) | +2 | He nucleus (particle) | Least | Sheet of paper |
| Beta (β) | −1 | Fast electrons (particle) | Medium | Thin metal sheet |
| Gamma (γ) | 0 | Electromagnetic waves (no mass) | Most (~2 MeV) | Thick lead / concrete |
Famous “Anchor Facts” — Most Tested in Exams
- Three subatomic particles — electron (−), proton (+), neutron (0).
- Atom proposed indivisible — Dalton’s atomic theory.
- Nucleus discovered — Rutherford’s gold-foil experiment (1911).
- Total elements — 118 confirmed; 92 occur naturally.
- Atomic number (Z) = number of protons (defines the element).
- Isotopes — same Z, different number of neutrons (e.g. C-12, C-13, C-14).
- Half-life of Carbon-14 — 5,730 years (used in radiocarbon dating).
- Uranium decay end-product — Lead (Pb).
- Fissile isotope of uranium — U-235.
- Most abundant uranium isotope in nature — U-238 (~99.3%).
- Atomic bomb — uncontrolled fission; nuclear reactor — controlled fission.
- Reactor coolant — liquid sodium; moderator/reflector — graphite.
- Highly enriched isotopes produced by ultracentrifuge separation.
- Atomic energy comes from mass-to-energy conversion (E = mc²).
- Visible light wavelength — 3,900–7,600 Å (VIBGYOR / ROYGBIV).
- Shortest wavelength / highest energy in EM spectrum — Gamma rays.
- Old-writing readable by — Infrared rays.
- Polythene — polymerization of ethylene.
- Rusting = oxidation; oils → ghee = hydrogenation.
- Photosynthesis — endothermic; combustion — gives heat + light.
Exam tip: Lock six anchor facts and you cover 80% of all MCQs from this chapter — 3 subatomic particles, U-235 = fissile / U-238 = abundant, α < β < γ in penetration, C-14 half-life = 5,730 years, VIBGYOR rainbow, and rusting = oxidation.
Frequently Asked Questions
Electrons (negative), protons (positive) and neutrons (no charge). Protons and neutrons form the nucleus; electrons orbit in shells.
Atoms of the same element with the same number of protons but different numbers of neutrons — e.g. Carbon has C-12, C-13 and C-14.
U-235 sustains a chain reaction. U-238 is the most abundant uranium isotope in nature (~99.3%) but is not fissile under thermal neutrons.
Gamma rays — electromagnetic, no mass or charge; require thick lead or concrete shielding. Energy ~2 MeV; travel at speed of light.
5,730 years — half of the C-14 nuclei in any sample decay over this period. Used in radiocarbon dating of fossils and ancient artefacts.
Chemical change — rusting is an oxidation reaction: Iron + O₂ + H₂O → hydrated iron oxide (rust).
Yes — essential. Atoms & Radioactivity MCQs are tested in every One Paper, NTS NAT, GAT, OTS, CTS, BPSC, KPPSC, SPSC, PPSC and FPSC exam — and core CSS Screening MPT (General Science & Ability) content.
Yes. Click the Download PDF button to get all Atoms, Radioactivity & Reactions MCQs as a branded QuizWing PDF for offline revision.