Q.Compare alpha particles, beta particles and gamma rays with respect to their charge, mass, speed and penetrating power.

Showing the 12 most recent of 26 on this concept.

1. CBSE 2026Set A1 markMCQ
   Q.Radioactivity was discovered by (A) Marie Curie (B) Pierre Curie (C) Ernest Rutherford (D) Henri Becquerel

   ›Reveal solutionSolution

   Radioactivity was discovered by Henri Becquerel in 1896.

   In 1896 Henri Becquerel found that uranium salts spontaneously emitted a penetrating radiation that fogged photographic plates even in the dark, without any external excitation. This spontaneous emission was named radioactivity. Marie and Pierre Curie later extended the work by isolating polonium and radium, and Rutherford classified the radiations into alpha, beta and gamma — but the original discovery of the phenomenon belongs to Becquerel.

   ✓Final answer

   (D) Henri Becquerel.

2. CBSE 2026Set ANNUAL1 mark
   Q.Write True or False: In γ-decay low energy photons are emitted.

   ›Reveal solutionSolution

   False — γ-decay emits HIGH energy photons.

   After an alpha or beta decay, a daughter nucleus is often left in an excited (higher energy) state. It reaches the ground state by emitting the excess energy as an electromagnetic photon — a gamma ray. Because the energy differences between nuclear levels are very large (of the order of MeV), these gamma photons are of very high energy (and very short wavelength).

   So the statement that low energy photons are emitted in γ-decay is False.

   ✓Final answer

   False (γ-decay emits high-energy photons).

3. CBSE 2025Set D1 markMCQ
   Q.Which one of the following is not a type of radioactive decay? (A) Alpha decay (B) Beta decay (C) Gamma decay (D) Muon decay

   ›Reveal solutionSolution

   The three radioactive decays of a nucleus are alpha, beta and gamma; muon decay is not one of them.

   Radioactivity is the spontaneous disintegration of an unstable nucleus. It occurs by three modes:

   • Alpha (α) decay — emission of a helium nucleus (⁴₂He).
   • Beta (β) decay — emission of an electron (β⁻) or positron (β⁺) with a neutrino/antineutrino.
   • Gamma (γ) decay — emission of a high-energy photon as an excited nucleus de-excites.

   A muon is an elementary lepton; its own decay is a particle-physics process, not a mode of nuclear radioactive decay.

   ✓Final answer

   (D) Muon decay.

4. CBSE 2025Set D1 markMCQ
   Q.Which of the following is chargeless particle? (A) α-particle (B) β-particle (C) Proton (D) Photon

   ›Reveal solutionSolution

   Among the listed particles only the photon is chargeless.

   Checking each:

   • α-particle — a helium nucleus, charge +2e.
   • β-particle — an electron, charge −e.
   • Proton — charge +e.
   • Photon — the quantum of electromagnetic radiation, charge zero (and rest mass zero).

   Hence the only chargeless particle is the photon.

   ✓Final answer

   (D) Photon.

5. CBSE 2025Set ANNUAL1 markMCQ
   Q.Which of the following particle has mass equal to that of electron ?

   (a) neutron

   (b) proton

   (c) positron

   (d) neutrino

   ›Reveal solutionSolution

   The positron is the antiparticle of the electron: identical mass, opposite (positive) charge.

   A positron ($e^+$, emitted for instance in $\beta^+$ decay of a proton-rich nucleus) has exactly the same rest mass as an electron ($m_e \approx 9.11\times10^{-31}$ kg), but carries a charge of $+e$ instead of $-e$. Neutrons and protons are both far more massive (~1836–1839 times $m_e$), and a neutrino's mass is extremely small (near-zero), not equal to the electron's.

   ✓Final answer

   (c) positron.

6. CBSE 2024Set A11 mark
   Q.Alpha particle is a ———————— nucleus. Fill in the blank choosing the appropriate answer from the bracket: (decreasing, interference, helium, greater, diffraction, increasing)

   ›Reveal solutionSolution

   helium nucleus.

   ✓Final answer

   helium nucleus.

   An alpha particle is a doubly ionised helium nucleus $\left(^{4}_{2}\text{He}\right)$, consisting of 2 protons and 2 neutrons, carrying charge $+2e$.

7. CBSE 2024Set ANNUAL1 markMCQ
   Q.If a radioactive atom emits a beta-particle then its atomic mass

   (a) increases by one unit

   (b) remains unchanged

   (c) decreases by two units

   (d) increases by two units

   ›Reveal solutionSolution

   Beta-minus decay converts a neutron into a proton inside the nucleus, so the total nucleon count (mass number) is unchanged even though the atomic number increases by one.

   In beta-minus ($\beta^-$) decay, a neutron in the nucleus transforms into a proton, emitting an electron (the beta particle) and an antineutrino:

   $n \rightarrow p + e^- + \bar{\nu}$

   Symbolically, for a nucleus $^A_Z X \rightarrow {}^A_{Z+1} Y + e^- + \bar\nu$. Since a neutron is simply replaced by a proton, the total number of nucleons (mass number A = protons + neutrons) does not change - only the atomic number Z increases by 1 (the element changes, but the mass number is conserved). So the atomic mass (mass number) remains unchanged in beta decay - it is alpha decay that reduces the mass number by 4.

   ✓Final answer

   (b) remains unchanged.

8. CBSE 2023Set F1 markMCQ
   Q.Which of the following has the highest penetrating power? (A) alpha-rays (B) beta-rays (C) gamma-rays (D) Cathode rays

   ›Reveal solutionSolution

   γ-rays penetrate most; α least.

   Penetrating power increases as ionising power decreases:

   • α-rays (helium nuclei): heavily ionising, stopped by paper/skin — least penetrating.
   • β-rays (electrons): moderate, stopped by a few mm of aluminium.
   • γ-rays (high-energy photons): uncharged, need thick lead/concrete — most penetrating.

   Cathode rays are just electrons (like β), less penetrating than γ.

   ✓Final answer

   (C) gamma-rays.

9. CBSE 2023Set TERM21 markMCQ
   Q.Study the following paragraph and answer questions number 8 and 9 based on it: The Radioactive Nuclei are unstable and emit alpha (2He^4), beta (-1e^0) and gamma (0γ^0) radiations to achieve states of greater stability. Ruther-ford and Soddy suggested the following rules governing the Radioactive decay.

   (i) The algebraic sum of atomic numbers before and after disintegration must be same.

   (ii) The sum of mass numbers before and after disintegration must also be same. Choose the correct product of nuclear reaction: 90Th234 → 91Pa234 + ............

   (a) α (Alpha)

   (b) β (Beta)

   (c) γ (Gamma)

   (d) None of these.

   ›Reveal solutionSolution

   Balancing mass number and atomic number in ${}_{90}\text{Th}^{234} \to {}_{91}\text{Pa}^{234} + X$ shows $X$ must be a $\beta$-particle (electron).

   By the Soddy–Fajans conservation rules given: mass number (A) is conserved and atomic number (Z) is conserved across the reaction.

   Mass number: $234 = 234 + A_X \Rightarrow A_X = 0$.

   Atomic number: $90 = 91 + Z_X \Rightarrow Z_X = -1$.

   A particle with mass number 0 and charge/atomic number $-1$ is exactly a beta particle, ${}_{-1}e^0$ (an electron emitted from the nucleus, converting a neutron into a proton and raising Z by one while leaving A unchanged).

   ✓Final answer

   (b) $\beta$ (Beta) particle — this is a $\beta^-$ decay: ${}_{90}\text{Th}^{234} \to {}_{91}\text{Pa}^{234} + {}_{-1}e^0 + \bar\nu$.

10. CBSE 2023Set TERM21 markMCQ
    Q.Based on the radioactive-decay passage above (Q.8): In alpha (α) decay, A is mass number and Z is atomic number.

    (a) A decreases by 4 and Z increases by 2

    (b) A decreases by 4 and Z decreases by 2

    (c) A increases by 4 and Z decreases by 2

    (d) A increases by 4 and Z increases by 2.

    ›Reveal solutionSolution

    An alpha particle is a helium nucleus, ${}_2\text{He}^4$, so emitting one removes 4 from the mass number and 2 from the atomic number.

    Alpha decay is the emission of an alpha particle, ${}_2\text{He}^4$, which itself has mass number 4 and atomic number (charge number) 2. By conservation of A and Z (as stated in the passage):

    ${}_Z X^A \to {}_{Z-2}Y^{A-4} + {}_2\text{He}^4$

    So the mass number of the daughter nucleus is 4 less than the parent, and its atomic number is 2 less than the parent's.

    ✓Final answer

    (b) A decreases by 4 and Z decreases by 2.

11. CBSE 2023Set ANNUAL1 markMCQ
    Q.In a given reaction : zX^A → (z+1)Y^A → (z-1)K^(A-4) → (z-1)K^(A-4), the radioactive radiations are emitted in the sequence of –

    (a) α, β, γ

    (b) γ, α, β

    (c) β, α, γ

    (d) γ, β, α

    ›Reveal solutionSolution

    Track how Z and A change at each step of the decay chain: an increase in Z with same A is β⁻ decay; a drop of 2 in Z with a drop of 4 in A is α decay; no change in Z or A but a distinct final state is γ emission.

    Why / steps:

    1. $_{Z}X^{A}\to {}_{Z+1}Y^{A}$: mass number unchanged, atomic number increases by 1 → this is β⁻ decay (a neutron converts to a proton, emitting an electron and an antineutrino).

    2. $_{Z+1}Y^{A}\to {}_{Z-1}K^{A-4}$: atomic number drops by 2, mass number drops by 4 → this is α decay (loss of a helium-4 nucleus).

    3. The final step keeps the same $_{Z-1}K^{A-4}$ nucleus (same Z, same A) — a nucleus formed in an excited state simply drops to its ground state by emitting a γ-ray photon, with no change in Z or A.

    ✓Final answer

    The sequence of emissions is β, α, γ — option (c).

12. CBSE 2023Set ANNUAL1 markMCQ
    Q.During alpha-decay, mass number ________ by ________.

    (a) decreases, 2

    (b) increases, 2

    (c) decreases, 4

    (d) increases, 4

    ›Reveal solutionSolution

    In alpha decay the mass number decreases by 4.

    An alpha particle is a helium nucleus, 2 protons and 2 neutrons (mass number 4, charge +2). When a nucleus emits it, the parent loses 4 nucleons and 2 protons: mass number A decreases by 4 and atomic number Z decreases by 2. For example, uranium-238 decays to thorium-234. This is standard NCERT/CBSE Class 12 nuclear physics.

    ✓Final answer

    (c) decreases, 4.