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ρ = 10¹⁷ Kg/m³ nuclear density remains constant. 

The half-life of a radioactive substance is a characteristic constant. It measures the time it takes for a given amount of the substance to become reduced by half as a consequence of decay, and therefore, the emission of radiation. 

(c) the containers will in general have different numbers of the atoms of the material but their average will be close to 5000. 

(i) Keen observer / helpful / concerned / responsible / respectful towards elders.(Any two)

(ii)The doctor can trace and observe the difference between the moment of an appropriate radio isotope through a normal  brain and a brain having tumour in it.

(i) γ-rays are photons of very short wavelength of the order of 10-¹¹ m to 10^-13 m.

(ii) γ-rays are not deflected by the electric field and the magnetic field.

(iii) γ-rays carry no charge.

(iv) γ-rays move with the speed of light.

(v) γ-rays affect the photographic plate.

(vi) The penetrating power of  γ-rays is about 100 times more than that of α-rays.

(vii) The ionising power of γ-rays is about 1/ 100^th of that of β-rays.

(viii)γ-rays can cause fluorescence.

(ix) γ-rays are diffracted by the crystals and can cause photoelectric emission from metals of high atomic weight

Properties of  α-rays :

(i) α-rays consist of doubly ionised heliurn atoms.

(ii) α-rays are deflected by the electric field and the magnetic field.

(iii)  α-rays carry positive charge of 3.2 x 10^-19 C

(iv) The velocity of  α-rays is about 10% of the velocity of light.

(.r) o-rays affect the photographic plate.

(vi)  α-rays are absorbed by thin foils. For example, an aluminium foil 0.01 cm thick is sufficient to absorb them. In air  at normal pressure, they may penetrate up to 3 to 4 cm.

(vii) α-rays ionise the gas through which they pass. A single α- parficle can ionise even up to 20,000 gas atoms.

(viii) α- rays fluorescence in zinc sulphide, barium platinocyanide, etc.

(ix)  α- rays get scattered by the thin foils.

Class 12 Physics has many MCQ Questions for problem-solving and practicing. Thus, there are high chances that a number of new MCQ Questions for class 12 might be given in the examination, keeping these questions as the base. Let’s look various MCQ Questions for class 12 Physics Nuclei for exam preparation. It helps to understand the Exam Pattern and Questions asked in the exams.

Most of the Class 12 Physics MCQ Questions of Nuclei with Answers are further extensions that’s why students look for mostly Chapter 13 Nuclei which are accurate and solved with simplification. This Chapter 13 Nuclei includes multiple numbers and makes the calculation process a little bit difficult.

Practice MCQ Question for Class 12 Physics chapter-wise

1. Chadwick was awarded the Nobel prize in Physics in 1935 for his discovery of:

(a) electron
(b) proton
(c) neutron
(d) None of these

2. The density of a nucleus is of the order of:

(a) 10¹⁵ kg m^-3
(b) 10¹⁸ kg m^-3
(c) 10¹⁷ kg m^-3
(d) 10¹⁶ kg m^-3

3. Alpha particle emitted from a radioactive material are:

(a) Helium nuclei
(b) Hydrogen nuclei
(c) Lithium nuclei
(d) None of the above

4. Which of the following atoms has the lowest ionization potential?

(a) ₈O⁸
(b) ₇N¹⁴
(c) ₅₅Cs¹³³
(d) ₁₈Ar⁴⁰

5. X-ray was discovered by :

(a) Becqueral
(b) Marie curie
(c) Roengton
(d) Vanlaw

6. Fusion takes place at high temperature because:

(a) Atom are ionised at high temperature
(b) Molecules break up at high temperature
(c) Nuclei break up at high temp.
(d) Kinetic energy is high enough to overcome repulsion between nuclei

7. The isotope generally used for the treatment of cancer is:

(a) I¹³¹
(b) Hg¹⁹⁷
(c) O¹⁵
(d) Co⁶⁰

8. What percentage of radioactive substance is left after 5 half lives?

(a) 3.125%
(b) 6.25%
(c) 12.33%
(d) 31%​

9. ​​​​​​The helium atom does not contain

(a) two protons
(b) two electrons
(c) two neutrons
(d) six nucleons

10. The phenomena of radioactivity is:

(a) Exothermic change with increase or decrease with temperature
(b) increases on applied pressure
(c) nuclear process does not depend on external factors
(d) None of these

11. The quantity which is not conserved in a nuclear reaction is

(a) momentum
(b) charge
(c) mass
(d) none of these

12. Ratio of the radii of the nuclei with mass numbers 8 and 27 would be

(a) \(\frac{27}{8}\)
(b) \(\frac{8}{27}\)
(c) \(\frac{2}{3}\)
(d) \(\frac{3}{2}\)​

13. ​​​​​​A radioactive nucleus emits a beta particle. The parent and daughter nuclei are

(a) isotopes
(b) isotones
(c) isomers
(d) isobars

14. An electron emitted in beta radiation originates from

(a) inner orbits of atom
(b) free electrons existing in the nuclei
(c) decay of a neutron in a nuclei
(d) photon escaping from the nucleus

15. Complete the series 6He → e^– + 6Li⁺

(a) neutrino
(b) antineutrino
(c) proton
(d) neutron

16. Light energy emitted by star is due to

(a) breaking of nuclei
(b) joining of nuclei
(c) burning of nuclei
(d) reflection of solar light

17. In nuclear reactors, the control rods are made of

(a) cadmium
(b) graphite
(c) krypton
(d) plutonium

18. Radioactivity is the phenomenon associated with

(a) decay of nucleus
(b) production of radio waves
(c) transmission of radio waves
(d) reception of radio waves

19. Sun’s radiant energy is due to

(a) nuclear fission
(b) nuclear fusion
(c) photoelectric effect
(d) spontaneous radioactive decay

20. Isotones have the same number of _________ .

(a) neutrons
(b) protons
(c) electrons
(d) all of these

21. Fusion reaction takes place at high temperature because

(a) atoms get ionised at high temperature
(b) kinetic energy is high enough to overcome the Coulomb repulsion between nuclei
(c) molecules break up at high temperature
(d) nuclei break up at high temperature

22.  Of the various series of the hydrogen spectrum, which of the following lies wholly in the ultraviolet region?

(a) Balmer Series
(b) Paschen Series
(c) Brackett series
(d) Lyman Series

23. \(\gamma\)-rays are originated from

(a) nucleus
(b) outermost shell of nucleus
(c) innermost shell of nucleus
(d) outermost shell of atom

24. The binding energy per nucleon for the parent nucleus is E₁ and that for the daughter nuclei is E₂. Then

(a) E₁ > E₂
(b) E₂ > E₁
(c) E₁ = 2E₂
(d) E₂ = 2E₁

25. A set of nuclides that have a different number of protons and neutrons, but there is the same difference between the protons and neutrons is called as

(a) Isobar
(b) Isotone
(c) Isotop
(d) Isodiaphers

Answer: 

1. Answer : (c) neutron

Explanation: The Nobel Prize in Physics 1935 was awarded to James Chadwick "for the discovery of the neutron."

2. Answer : (c) 10¹⁷ kg m^-3

Explanation: Nuclear density is the density of the nucleus of an atom, averaging about 2.3 \(\times\)10¹⁷ kg/m³. The descriptive term nuclear density is also applied to situations where similarly high densities occur, such as within neutron stars. The experimentally determined value for n is 0.16 fm⁻³, that is 1.6·1044 m⁻³.

3. Answer : (a) Helium nuclei

Explanation: Alpha particles are helium nuclei (two protons, two neutrons) emitted mostly by heavy nuclei .The mass number of the parent nucleus is reduced by 4.

4. Answer : (c) ₅₅Cs¹³³

Explanation: Since  ₅₅Cs¹³³ has larger size among the four atoms given, thus the electrons present in the outermost orbit will be away from the nucleus and the electrostatic force experienced by electrons due to nucleus will be minimum. Therefore the energy required to liberate electron from outer orbit will be minimum in the case of  ₅₅Cs¹³³.

5. Answer : (c) Roengton

Explanation: W.C. Röntgen reported the discovery of X-rays in December 1895 after seven weeks of assiduous work during which he had studied the properties of this new type of radiation able to go through screens of notable thickness.

6. Answer : (d) Kinetic energy is high enough to overcome repulsion between nuclei

Explanation: This happens because at high temperature, there is enough kinetic energy to overcome the repulsion and the strong interaction pulling the protons together is stronger than repulsion pushing the protons apart, the atoms will fuse together forming a new atom containing protons of both atoms we pushed together.

7. Answer : (d) Co⁶⁰

Explanation: Cobalt therapy or cobalt - 60 therapy is the medical use of gamma rays from the radioisotope cobalt 60 to treat conditions such as cancer. 

8. Answer : (a) 3.125%

Explanation: 

\(\frac{N}{N_0}=\)​ \((\frac{1}{2})^5\)

\(=\frac{1}{32}\)

\(=\frac{1}{3^2}\)

\(=M\frac{100}{32}\)​

9. Answer : (d) six nucleons

Explanation: Helium contain 2 protons, 2 electrons and 2 neutrons.

10. Answer : (c) nuclear process does not depend on external factors

Explanation:  Radioactivity is the phenomenon of the spontaneous disintegration of unstable atomic nuclei to atomic nuclei to form more energetically stable atomic nuclei.

11. Answer : (c) mass

Explanation: In a nuclear reaction, mass is not conserved. The difference in masses of reactants and product nuclei, known as the mass defect is converted to an equivalent amount of energy according to Einstien's equation E = mc²

12. Answer : (c) 

Explanation: 

\(r\propto A^{\frac{1}{3}}\)

\(\therefore \frac{r_8}{r_{27}}=3\sqrt{\frac{8}{27}}\)

\(=\frac{2}{3}\)​

13. ​​​​​​Answer : (d) isobars

Explanation: A radioactive nucleus emits beta particle. The parent and daughter nuclei are isobars.

14. Answer : (c) decay of a neutron in a nuclei

Explanation: During (\(\beta\) -decay, a neutron is transformed into a proton and an electron. This is why atomic number (Z = number of protons) increases by one and mass number (A = number of protons + neutrons) remains unchanged during beta decay.

15. Answer : (b) antineutrino

Explanation: ⁶He → e⁻ + ⁶Li + v⁻ 

16. Answer : (b) joining of nuclei

Explanation: Light energy emitted by stars is due to fusion of light nuclei.

17.  Answer : (a) cadmium

Explanation: Control rods are made up of cross-section to stop neutrons of various energies. It made up of Boron, Cadmium, Silver and Indium to control the rate of nuclear fission.

18. Answer : (a) decay of nucleus

Explanation: In all these processes there is a decay of the nucleus; this means the process of radioactivity is associated with the decay of the nucleus.

19. Answer : (b) nuclear fusion

Explanation: The sun generates energy from a process called nuclear fusion. During nuclear fusion, the high pressure and temperature in the sun's core cause nuclei to separate from their electrons.

20. Answer : (a) neutrons

Explanation: Isotones are atomic species that share the same number of neutrons and differ in the number of protons. Examples carbon-12, nitrogen-13 and oxygen-14. These atoms all have six neutrons and six, seven and eight protons respectively.

21. Answer : (b) kinetic energy is high enough to overcome the Coulomb repulsion between nuclei

Explanation: Thermal K.E.\(\geq\) Electrostatic P.E.

22.  Answer : (d) Lyman Series

Explanation: Lyman series lies in the UV region.

23. Answer :(a) nucleus

Explanation: When an alpha or a beta decay takes place, the daughter nucleus is generally formed in one of its excited states eventually comes to its ground state by emitting a photon or photons of electromagnetic radiation. The process of a nucleus coming down to a lower energy level by emitting a photon is called gamma decay. Hence \(\gamma\) − rays are originated from excited nucleus.

24. Answer : (b) E₂ > E₂

Explanation: When a heavy nucleus of higher mass number (less stable) splits into two lighter nuclei the daughter nucleus is of less mass number and becomes more stable, having more binding energy per nucleon. Therefore, E₂ > E₂

25. Answer : (d) Isodiaphers

Explanation: Isodiaphers are a set of nuclides that have a different number of protons and neutrons, but there is the same difference between the protons and neutrons.

Example of isodiaphers

Thorium – 234 and Uranium – 238

Protons in Thorium is 90

Neutrons in Thorium is 144

= 144 – 90

= 54

Protons in Uranium is 92

Neutrons in Uranium is 146

The difference between neutrons and protons in Uranium

146 – 92

= 54

The difference between neutrons and protons in Thorium and Uranium is the same, so it is an example of isodiaphers.

Click here to practice  MCQ Question for Nuclei Class 12

The nuclear mass M is always less than the total mass of its constituents. The difference in mass of a nucleus and its constituents ΔM is called the mass defect, 

ΔM = (Z m_p + (A – Z)m_n) – M 

Using Einstein’s mass energy relation, we express this mass difference in terms of energy as 

ΔE_b = ΔM c² 

The energy ΔE_b represents the binding energy of the nucleus. In the mass number range A = 30 to 170, the binding energy per nucleon is nearly constant, about 8 MeV/nucleon. 

Example : 

The atomic mass of nucleus of ¹⁶₈O found from mass spectroscopy experiments is seen to be 15.99053 u. The expected mass of ¹⁶₈O nucleus is by adding 8 protons mass and 8 neutrons mass = 16.12744 u. 

The difference between these two masses is mass defect = 0.13691 u. 

1. beta particle – 1, 3, 8

2. Gama ray – 2, 6 

3. alpha particle – 3, 4, 7

1. Mass of nucleus = (8 × 1.00864 + 8 × 1.007274) amu.

2. (8 × 1.00864 + 8 × 1.007214 + 8 × 0.0055)amu

3. ∆m = [ZM_p + (A - Z) M_n – M)

4. When two light nuclei are combined to form a heavy nucleus, the binding per nucleon increases. Hence the stability of atom increases. When heavy nucleus split into two light nuclei; B.E. for nucleon also increases.