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Structure of Atoms and Nuclei — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Structure of Atoms and Nuclei MCQs with step-by-step solutions covering Rutherford's Model & Atomic Structure, Bohr's Model & Energy Levels, Hydrogen Spectrum, Nuclear Size, Mass & Composition, Mass Defect & Binding Energy, Radioactivity & Decay Law. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Rutherford's Model & Atomic Structure · easy · theory
Rutherford's alpha particle scattering experiment used a thin foil of:
A. Gold ✓ Correct
B. Iron
C. Lead
D. Aluminium
Solution: Gold can be beaten into extremely thin foil, only a few hundred atoms thick, so multiple scattering is negligible.
Q2 — Rutherford's Model & Atomic Structure · easy · theory
In the alpha scattering experiment, most of the alpha particles passed through the foil undeviated. This showed that:
A. Electrons are heavier than alpha particles
B. The nucleus is negatively charged
C. The atom has a uniform positive charge
D. Most of the atom is empty space ✓ Correct
Solution: Only a tiny fraction of the incident particles encountered anything massive enough to deflect them.
Q3 — Rutherford's Model & Atomic Structure · easy · theory
The nucleus of an atom carries:
A. A negative charge
B. A positive charge ✓ Correct
C. A charge that varies with time
D. No charge
Solution: The protons within it give the nucleus a charge of $+Ze$.
Q4 — Rutherford's Model & Atomic Structure · easy · numerical
The charge on an alpha particle is:
A. $+4e$
B. $+e$
C. $-2e$
D. $+2e$ ✓ Correct
Solution: An alpha particle is a helium nucleus, containing two protons and two neutrons.
Q5 — Rutherford's Model & Atomic Structure · easy · numerical
The mass number of an alpha particle is:
A. $2$
B. $4$ ✓ Correct
C. $8$
D. $1$
Solution: Two protons plus two neutrons give a mass number of four.
Q6 — Bohr's Model & Energy Levels · easy · theory
According to Bohr's postulate, the orbital angular momentum of an electron in the $n^{\text{th}}$ orbit is:
A. $\dfrac{n^2h}{2\pi}$
B. $\dfrac{h}{2\pi n}$
C. $\dfrac{2\pi n}{h}$
D. $\dfrac{nh}{2\pi}$ ✓ Correct
Solution: Only orbits satisfying this quantisation condition are allowed.
Q7 — Bohr's Model & Energy Levels · easy · theory
According to Bohr's model, an electron revolving in a stationary orbit:
A. Radiates energy continuously
B. Does not radiate energy ✓ Correct
C. Absorbs energy continuously
D. Loses mass steadily
Solution: This postulate was introduced precisely to rescue the atom from classical collapse.
Q8 — Bohr's Model & Energy Levels · easy · theory
Radiation is emitted by an atom when an electron:
A. Jumps from a lower level to a higher one
B. Jumps from a higher energy level to a lower one ✓ Correct
C. Leaves the atom entirely
D. Remains in a stationary orbit
Solution: The photon energy is exactly the difference between the two levels, $h\nu = E_2 - E_1$.
Q9 — Bohr's Model & Energy Levels · easy · theory
The radius of the first Bohr orbit of hydrogen is approximately:
A. $0.053\text{ \AA}$
B. $1.06\text{ \AA}$
C. $0.53\text{ \AA}$ ✓ Correct
D. $5.3\text{ \AA}$
Solution: This value, $5.3 \times 10^{-11}\text{ m}$, is known as the Bohr radius.
Q10 — Bohr's Model & Energy Levels · easy · theory
The energy of the electron in the ground state of hydrogen is:
A. $-27.2\text{ eV}$
B. $+13.6\text{ eV}$
C. $-3.4\text{ eV}$
D. $-13.6\text{ eV}$ ✓ Correct
Solution: The negative sign indicates that the electron is bound to the nucleus.
Q11 — Bohr's Model & Energy Levels · easy · numerical
The radius of the first Bohr orbit of hydrogen is $r_0$. The radius of the third orbit is:
A. $9r_0$ ✓ Correct
B. $3r_0$
C. $6r_0$
D. $\dfrac{r_0}{9}$
Solution: $r_n \propto n^2$, so $r_3 = 9r_0$.
Q12 — Bohr's Model & Energy Levels · easy · numerical
The energy of an electron in the first excited state ($n = 2$) of hydrogen is:
A. $-6.8\text{ eV}$
B. $-3.4\text{ eV}$ ✓ Correct
C. $-1.51\text{ eV}$
D. $-13.6\text{ eV}$
Solution: $E_2 = -\dfrac{13.6}{4} = -3.4\text{ eV}$.
Q13 — Bohr's Model & Energy Levels · easy · numerical
The energy required to ionise a hydrogen atom from its ground state is:
A. $3.4\text{ eV}$
B. $27.2\text{ eV}$
C. $13.6\text{ eV}$ ✓ Correct
D. $10.2\text{ eV}$
Solution: Ionisation means raising the electron from $-13.6\text{ eV}$ to zero energy.
Q14 — Hydrogen Spectrum · easy · theory
The Lyman series of the hydrogen spectrum lies in the:
A. Visible region
B. Microwave region
C. Infrared region
D. Ultraviolet region ✓ Correct
Solution: All Lyman transitions end at $n = 1$ and so involve the largest energy differences.
Q15 — Hydrogen Spectrum · easy · theory
The Balmer series of the hydrogen spectrum lies mainly in the:
A. Visible region ✓ Correct
B. Infrared region
C. X-ray region
D. Ultraviolet region
Solution: Transitions ending at $n = 2$ give the familiar red, blue-green and violet hydrogen lines.
Q16 — Hydrogen Spectrum · easy · theory
The Paschen series of the hydrogen spectrum lies in the:
A. Ultraviolet region
B. Visible region
C. Gamma ray region
D. Infrared region ✓ Correct
Solution: These transitions terminate at $n = 3$ and involve comparatively small energy differences.
Q17 — Nuclear Size, Mass & Composition · easy · theory
The nucleus of an atom is composed of:
A. Protons and electrons
B. Protons and neutrons ✓ Correct
C. Neutrons and electrons
D. Only protons
Solution: Collectively protons and neutrons are called nucleons.
Q18 — Nuclear Size, Mass & Composition · easy · theory
The mass number $A$, atomic number $Z$ and neutron number $N$ are related by:
A. $A = Z + N$ ✓ Correct
B. $N = A + Z$
C. $A = Z - N$
D. $A = ZN$
Solution: The mass number simply counts the total number of nucleons.
Q19 — Nuclear Size, Mass & Composition · easy · theory
Isotopes of an element are nuclides having:
A. The same atomic number but different mass numbers ✓ Correct
B. The same mass number but different atomic numbers
C. The same number of nucleons and protons
D. The same number of neutrons
Solution: Isotopes are chemically identical but differ in nuclear mass, for example $^{12}\text{C}$ and $^{14}\text{C}$.
Q20 — Nuclear Size, Mass & Composition · easy · theory
One atomic mass unit is equivalent to an energy of approximately:
A. $931.5\text{ MeV}$ ✓ Correct
B. $13.6\text{ MeV}$
C. $1.6 \times 10^{-19}\text{ MeV}$
D. $931.5\text{ eV}$
Solution: This conversion follows from $E = mc^2$ and makes nuclear energy calculations straightforward.
Q21 — Nuclear Size, Mass & Composition · easy · numerical
The number of neutrons in a nucleus of mass number $A$ and atomic number $Z$ is:
A. $Z$
B. $\dfrac{A}{Z}$
C. $A - Z$ ✓ Correct
D. $A + Z$
Solution: The protons number $Z$ and the rest of the nucleons are neutrons.
Q22 — Nuclear Size, Mass & Composition · easy · numerical
An energy of $1\text{ u}$ of mass defect corresponds to:
A. $93.15\text{ MeV}$
B. $9315\text{ MeV}$
C. $1.5\text{ MeV}$
D. $931.5\text{ MeV}$ ✓ Correct
Solution: This is the standard conversion used in all binding energy calculations.
Q23 — Mass Defect & Binding Energy · easy · theory
The mass defect of a nucleus is:
A. The difference between the sum of the masses of the free nucleons and the mass of the nucleus ✓ Correct
B. The difference between proton and neutron masses
C. The mass of the nucleus alone
D. The mass of the electrons in the atom
Solution: This missing mass has been converted into the binding energy that holds the nucleus together.
Q24 — Mass Defect & Binding Energy · easy · theory
The binding energy of a nucleus is related to its mass defect by:
A. $BE = \Delta m\,c$
B. $BE = \Delta m\,c^2$ ✓ Correct
C. $BE = \dfrac{\Delta m}{c^2}$
D. $BE = \dfrac{c^2}{\Delta m}$
Solution: It is the energy that would be needed to separate the nucleus completely into free nucleons.
Q25 — Mass Defect & Binding Energy · easy · theory
A nucleus with a higher binding energy per nucleon is:
A. More stable ✓ Correct
B. Less stable
C. Radioactive always
D. Larger in size
Solution: More energy per nucleon must be supplied to break it apart.
Q26 — Mass Defect & Binding Energy · easy · numerical
Two nuclei have binding energies per nucleon of $7.5\text{ MeV}$ and $8.5\text{ MeV}$. The more stable one is:
A. Neither is stable
B. Both are equally stable
C. The nucleus with $7.5\text{ MeV}$ per nucleon
D. The nucleus with $8.5\text{ MeV}$ per nucleon ✓ Correct
Solution: Greater binding energy per nucleon means the nucleons are held more tightly.
Q27 — Radioactivity & Decay Law · easy · theory
In alpha decay, the mass number and atomic number of the nucleus change by:
A. $-2$ and $-4$ respectively
B. $-4$ and $-2$ respectively ✓ Correct
C. $-4$ and $+2$ respectively
D. $0$ and $+1$ respectively
Solution: An alpha particle carries away two protons and two neutrons.
Q28 — Radioactivity & Decay Law · easy · theory
In gamma emission, the mass number and atomic number of the nucleus:
A. Both remain unchanged ✓ Correct
B. Both increase
C. Both decrease
D. Change by $-4$ and $-2$
Solution: Gamma emission merely carries away excess energy from an excited nucleus.
Q29 — Radioactivity & Decay Law · easy · theory
The radioactive decay law is expressed as:
A. $N = N_0e^{-\lambda t}$ ✓ Correct
B. $N = N_0\lambda t$
C. $N = \dfrac{N_0}{\lambda t}$
D. $N = N_0e^{\lambda t}$
Solution: The decay is exponential, with $\lambda$ the decay constant characteristic of the nuclide.
Q30 — Radioactivity & Decay Law · easy · theory
The half-life and decay constant of a radioactive nuclide are related by:
A. $T_{1/2} = \dfrac{0.693}{\lambda}$ ✓ Correct
B. $T_{1/2} = \dfrac{1}{\lambda}$
C. $T_{1/2} = 0.693\lambda$
D. $T_{1/2} = \dfrac{\lambda}{0.693}$
Solution: Setting $N = \dfrac{N_0}{2}$ in the decay law gives $T_{1/2} = \dfrac{\ln 2}{\lambda}$.