Nuclei

Nuclei Class 12 MCQs Questions with Answers

Question 1.
Beta rays emitted by a radioactive material are
(a) neutral particles.
(b) charged particles emitted by nucleus.
(c) electromagnetic radiations.
(d) electrons orbiting around the nucleus.

Question 2
How much energy will approximately be released if all the atoms of 1 kg of deuterium could undergo fusion?
(a) 2 × 10⁷ kWh
(b) 9 × 10¹³J
(c) 6 × 10²⁷ Cal
(d) 8 × 10²³ MeV.

Question 3.
The packing fraction for \(_{7}^{14}\)N isotope whose mass is 14.003 amu is:
(a) 0.9
(b) 7.8 × 10^-3
(c) 1.0002
(d) 2.1 × 10^-4

Question 4.
The binding energy per nucleon is almost constant for many nuclei. It shows that nuclear forces are
(a) Charge independent
(b) saturated in nature
(c) short range in nature
(d) attractive in nature

Question 5.
The binding energies per nucleon for a deutron and an α- particle are x₁ and x₂ respectively. The energy Q released in reaction
1H² + 1H² → \(_{2}^{4}\)He + Q is
(a) 4 (x₁ + x₂)
(b) 4 (x₁ – x₂)
(c) 2 (x₁ + x₂)
(d) 2 (X₁ – x₂).

Question 6.
The binding energies of the atoms of elements A and B are E_a and E_b respectively. Three atoms of the elements B fuse to give one atom of element A. This fusion process is accompained by release of energy E. Then E_a, E_b and E are related to each other as:
(a) E_a + E = 3 E_b
(b) E_a = 3E_b
(c) E_a – E = 3 E_b
(d) E_a + 3E_b + E = 0

Question 7.
Let m_n and m_p be the masses of a neutron and a proton respectively. M₁ and M₂ are the masses of a \(_{10}^{20}\)Ne nucleus and a \(_{20}^{40}\)Ca nucleus respectively. Then
(a) M₂ < 2M₁
(b) M₂ > 2M₁
(c) M₂ = 2M₁
(d) M₁ < 10 (m_n + m_p).

Question 8.
One requires an energy E_n to remove a nucleon from a nucleus and an energy E_e to remove an electron from an atom. Then
(a) E_n = E_e
(b) E_n > E_e
(c) E_n < E_e
(d) E_n > E_e.

Question 9.
When the number of nucleons in nuclei increases, the binding energy per nucleon numerically
(a) increases continuously with mass number.
(b) decreases continuously with mass number.
(c) First increases and then decreases with increase of mass number.
(d) Remains constant with mass number.

Question 10.
For an atomic reactor being critical, the ratio (k) of the average number of neutrons produced and used in chain reaction
(a) depends upon the mass of the fissionable material.
(b) is greater than one.
(c) is less than one.
(d) is equal to one.

Question 11.
Maximum permissible radiation dose a a person may have with no adverse effects is
(a) 250 × 10^-1 roentgen’s per week.
(b) 250 × 10^-2 roentgen’s per week.
(c) 250 × 10^-3 roentgen’s per week.
(d) 250 roentgen’s per week.

Question 12.
For thorium A = 232 and Z = 90. At the end of some radioactive disintegrations we obtain an isotope of lead with \(_{82}^{208}\)pb. Then the number of emitted α and ß particles are
(a) α = 4, ß = 6
(b) α = 5, ß = 5
(c) α = 6, ß = 4
(d) α = 6, ß = 6

Question 13.
If 10 % of a radioactive material decays in 5 days, then the amount of the original material left after 20 days is nearly.
(a) 60%
(c) 75%
(b) 70%
(d) 66%

Question 14.
If the atomic masses for the parent and daughter element in a radioactive decay are M_p and M_d and the mass of the electron m_e then the Q-value for the radioactive ß decay is given by
(a) Q = M_p C²
(b) Q = (M_p – M_d – M_c) C²
(c) Q = (M_p – M_d)C²
(d) Q = (M_p – m_d – 2M_e)C².

Question 15.
For the fission of heavy nucleus, neutron is more effective than the proton or a particle because
(a) Neutron is heavier than α-particle.
(b) Neutron is lighter than α-particle.
(c) Neutron moves with a small velocity.
(d) Neutron is uncharged.

Question 16.
Which of the following is the best nuclear fuel.
(a) Thorium-236
(b) Plutonium – 239
(c) Neptunium-239
(d) Uranium-236.

Question 17.
The energy released in the fission of a single ₉₂U²³⁵nucleus is 200 MeV. The fission rate of ₉₂U²³⁵ fuelled reactor operating a power level of 5 Watt is
(a) 1.56 × 10¹⁴ per sec.
(b) 1.56 × 10¹⁷ per sec.
(c) 1.56 × 10²⁰ per sec.
(d) 1.56 × 10¹⁷ per sec

Question 18.
Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is to
(a) absorb neutrons and stop chain reaction
(b) To cool the reactor
(c) To slow down the neutrons to thermal energies.
(d) To control the energy released.

Question 19.
The volume of a nucleus is smaller than that of an atom by a factor of:
(a) 10
(b) 10⁵
(c) 10¹⁵
(d) 10¹⁰

Question 20.
Consider the fission reaction :
₉₆U ²³⁶→ x¹¹⁷ + Y¹¹⁷ + ₀n¹ + ₀n¹
i.e., two nuclei of same mass numbers 117 are formed plus two neutrons. The binding energy per nuclear of X and Y is 8.5 MeV whereas U²³⁶ is 7.6 MeV. The total energy liberated will be about:
(a) 2 MeV
(b) 20 MeV
(c) 2,000 MeV
(d) 200 MeV

Question 21.
Fusion reations place at high temp, because
(a) Kinetic energy is high enough to overcome repulsion between nuclei.
(b) Nuclei break up at high temperature.
(c) Atoms are ionised at high temperature.
(d) Molecules break up at high temperature.

Question 22.
Which of the following nuclei is most stable
(a) even-even
(b) odd-odd
(c) odd-even
(d) even-odd

Question 23.
How many electrons are contained in \(_{92}^{238}\)U nucleus?
(a) 92
(b) 146
(c) 238
(d) 0

Question 24.
Chadwick was awarded the Nobel prize in Physics in 1935 for his discovery of:
(a) electron
(b) proton
(c) neutron
(d) None of these

Question 25.
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

Question 26.
In the given reaction:
\(_{Z}^{A}\)X → \(_{Z+1}^{A}\) Y → \(_{Z-1}^{A-4}\) K → \(_{Z-1}^{A-4}\) K radioactive radiations are emitted in the sequence
(a) α, β, γ
(b) β, α, γ
(c) γ, α, β
(d) β, γ, α

Question 27.
When the mass of a sample of a radioactive substance decreases, the mean life of the sample:
(a) increases
(b) decreases
(c) remain unchanged
(d) first decreases then increases

Question 28.
Alpha particle emitted from a radioactive material are:
(a) Helium nuclei
(b) Hydrogen nuclei
(c) Lithium nuclei
(d) None of the above

Question 29.
The half life of a radioactive decay is n times its mean life, n is equal to:
(a) 0.6930
(b) 0.0693
(c) \(\frac{1}{0.6930}\)
(d) 0.3070

Question 30.
Rutherford is the unit of:
(a) radioactivity
(b) energy
(c) photoelectric current
(d) magnetic field

Question 31.
According to Yukawa’s theory of nuclear forces, the origin of nuclear force between nucleons is due to the exchange of
(a) mesons
(b) photons
(c) electrons
(d) positrons

Question 32.
An electron and a positron each having a mass equivalent to 0.53 MeV annihilate each other and produce a photon. The minimum energy of the photon is.
(a) 0.53 MeV
(b) 1.06 MeV
(c) 2.12 MeV
(d) zero

Question 33.
The wavelength of y-rays is of the order of:
(a) 10^-8 m
(b) 10^-5 m
(c) 10^-11 m
(d) 10^-22 m

Question 34.
Radius of 1st Bohr orbit is a₀ (= 0.529 Å) What is the radius of 2nd Bohr orbit?
(a) 10^-8
(b) 2a₀
(c) 4a₀
(d) 2√2a₀

Question 35.
The ground state energy of Hydrogen atom is -13.6 eV. What is the potential energy of electron in this state?
(a) 0 eV
(b) -13.6 eV
(c) 2 eV
(d) -27.2 eV

Question 36.
Which of the following atoms has the lowest ionization potential?
(a) \(_{8}^{8}\)O
(b) \(_{7}^{14}\)N
(c) \(_{55}^{133}\)Cs
(d) \(_{18}^{40}\)Ar

Question 37.
The Bohr model of atom:
(a) assumes that the angular momentum of electron is quantized
(b) uses Einstein’s photoelectric equation
(c) predicts continuous emission spectra for atoms
(d) predicts the same emission spectra for all types of atoms

Question 38.
Nuclear force is:
(a) strong, short range and charge independent force
(b) charge independent, attractive and long range force
(c) strong, charge dependent and short range attractive force
(d) long range, change dependent and attractive force

Question 39.
If radio active nuclei emits β-particle, then mass-number:
(a) increased by 1 unit
(b) decreases by 1 unit
(c) increases by 2 unit
(d) decreases by 2 unit

Question 40.
An alpha particle is emitted from \(_{88}\)Ra\(^{226}\), then the product nuclei has:
(a) Z = 84, A = 224
(b) Z = 86, A = 224
(c) Z = 86, A = 222
(d) Z = 82, A = 222

Question 41.
X-ray was discovered by :
(a) Becqueral
(b) Marie curie
(c) Roengton
(d) Vanlaw

Question 42.
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

Question 43.
The order of nuclear density is :
(a) 10³
(b) 10¹⁷
(c) 10⁶
(d) None

Question 44.
The isotope generally used for the treatment of cancer is:
(a) I¹³¹
(b) Hg¹⁹⁷
(c) O¹⁵
(d) Co⁶⁰

Question 45.
What percentage of radioactive substance is left after 5 half lives?
(a) 3.125%
(b) 6.25%
(c) 12.33%
(d) 31%

Question 46.
Mass is converted into energy according to the relation:
(a) E = me²
(b) E = mgh
(c) E = \(\frac{3}{2}\)me²
(d) E = \(\frac{mgH}{c^2}\)

Question 47.
The helium atom does not contain
(a) two protons
(b) two electrons
(c) two neutrons
(d) six nucleons

Question 48.
The more readily fissionable isotope of uranium has an atomic mass of:
(a) 234
(b) 235
(c) 236
(d) 238

Question 49.
Energy of electron in the 1st orbit of H-atom is:
(a) -13.6 MeV
(b) -13.6 eV
(c) -13.6 J
(d) 13.6 J

Question 50.
The mass no. of a nucleus is M and its atomic no. is Z. The number of neutrons in the nucleus is :
(a) M – Z
(b) M
(c) Z
(d) M + Z

Question 51.
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

Question 52.
When one gm of mass is converted into energy, it is equal to:
(a) 10³ kWh
(b)10⁹ kWh
(c) 10¹⁰ kWh
(d) 10¹¹ kWh

Fill in the Blanks

Question 1.
Atoms having the same ……………….. but different ……………….. are called isotopes.

Question 2.
The size of the nucleus varies as ……………….. power of mass number.

Question 3
……………….. is the process in which light nuclei fuse together to form a heavy nucleus.

Question 4.
In the fission of ²³⁵U nucleus on an average ……………….. neutrons are released.

Question 5.
In a nuclear reactor, heavy water is used as a ……………….. which slows down the neutrons.

Question 6.
The difference between ₉₂U²³⁵ and ₉₂U²³⁸ is that ₉₂U²³⁸ contains three more ……………….. and fission of ₉₂U ²³⁸is caused ……………….. by neutrons while fission of ₉₂U²³⁵ is caused by ……………….. neutrons.

Question 7.
The order of magnitude of the density of nuclear matter is ………………..

Question 8.
The average binding energy per nucleon for the nuclei lying in the middle of periodic table is nearly ………………..

Question 9.
Two deuterium nuclei can combine to form a ……………….. if they possess sufficiently

Question 10.
The average energy released per fission of ₉₂U²³⁵ is approximately ……………….. MeV.

Question 11.
Proton was discovered by ……………….. and neutron was discovered by ………………..

Question 12.
The ratio of the radii of the nuclei ₁₃Al²⁷ and ₅₂Te¹²⁵ is approximately ………………..

Question 13
……………….. was the fissionable material used in the bomb dropped at Nagasaki in 1945.

Question 14.
An element A decays into element C by a two step process:
A → B + ₂He⁴
B → C + 2e^–,
Then A and C are ………………..

Question 15.
The sun obtains its radiant energy from ………………..

Question 16.
The B.E. per nucleon is maximum for ………………..

Question 17.
Slow neutrons are incident on a sample of uranium containing both ₉₂U²³⁵ and ₉₂U²³⁵ isotopes, then only ……………….. atoms will undergo fission. .

Question 18.
The critical mass of the fissionable material is ………………..

Question 19.
The bulk of energy released in nuclear fission process appears as ………………..

Question 20.
In a given reascion:
^AX_Z → ^AY_Z-1 → ^A-4K_Z-1 → ^A-4K_Z-1
the radioactive radiations are emitted in.the sequence of ………………..

Question 21.
A positron has the same mass as ………………..

Question 22.
Neutrino is a particle with ………………..

Question 23.
Out of α, ß and γ radiations, ……………….. and ……………….. are affected by a magnetic field.