Nuclei Class 12 MCQs Questions with Answers
Nuclei Class 12 MCQ Chapter 13 Question 1.
The gravitational force between a H – atom and another particle of mass m will be given by Newton’s law:\(\begin{equation}\mathrm{F}=\mathrm{G} \frac{\mathrm{M} \cdot m}{r^{2}}\end{equation}\) , where r is in km and
(A) \(\begin{equation}\mathrm{M}=m_{\text {proton }}+m_{\text {electron }}\end{equation}\)
(B) \(\begin{equation}\mathrm{M}=m_{\text {proton }}+m_{\text {electron }}-\frac{\mathrm{B}}{c^{2}} \quad(\mathrm{~B}=13.6 \mathrm{eV})\end{equation}\)
(C) M is not related to the mass of the hydrogen atom.
(D)\(\begin{equation}\mathrm{M}=m_{\text {proton }}+m_{\text {electron}}-\frac{|\mathrm{V}|}{c^{2}}(|\mathrm{~V}|\end{equation}\)= magnitude of the potential energy of electron in the H-atom).
Answer:
(B) \(\begin{equation}\mathrm{M}=m_{\text {proton }}+m_{\text {electron }}-\frac{\mathrm{B}}{c^{2}} \quad(\mathrm{~B}=13.6 \mathrm{eV})\end{equation}\)
Explanation:
During formation of H – atom, some mass of nucleons convert into energy by the equation
\(\begin{equation}\mathrm{E}=m c^{2}\end{equation}\)
This energy is used to bind the nucleons along with nucleus. So mass of atom becomes slightly less than sum of actual masses of nucleons and electrons.
Actual mass of H – atom
\(\begin{equation}=\mathrm{M}_{p}+\mathrm{M}_{e}-\frac{\text { B.E. }}{c^{2}}\end{equation}\)
\(\begin{equation}\frac{\mathrm{B}}{c^{2}}\end{equation}\) = Binding energy
So, the binding energy of H atoms is 13.6 eV per atom.
Nuclear Chapter 13 MCQ Question 2.
Heavy stable nucleus have more neutrons than protons. This is because of the fact that
(A) neutrons are heavier than protons.
(B) electrostatic force between protons are repulsive.
(C) neutrons decay into protons through beta decay.
(D) nuclear forces between neutrons are weaker than that between protons.
Answer:
(B) electrostatic force between protons are repulsive.
Explanation:
Electrostatic force between proton – proton is repulsive which causes theinsfatbility of nucleus. So neutrons are more than the number of protons.
Nuclei Class 12 MCQ Chapter 13 Question 3.
Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into p + \(\begin{equation}\tilde{e}\end{equation}\) + v. If one of the neutrons in Tritium decays, it would transform into \(\begin{equation}{ }_{2} \mathrm{He}^{3}\end{equation}\) nucleus. This does not happen. This is because
(A) tritium energy is less than that of a \(\begin{equation}\mathrm{He}^{3}\end{equation}\) nucleus.
(B) the electron created in the beta decay process cannot remain in the nucleus.
(C) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not a \(\begin{equation}\mathrm{He}^{3}\end{equation}\) nucleus.
(D) because free neutrons decay due to external perturbations which is absent in a triton nucleus.
Answer:
(A) tritium energy is less than that of a \(\begin{equation}\mathrm{He}^{3}\end{equation}\) nucleus.
Explanation:
Tritium \(\begin{equation}
\left({ }_{1}^{3} \mathrm{H}\right)
\end{equation}\) has 1 proton and 2 neutrons.
If a neutron decays as, \(\begin{equation}
n \rightarrow p+\bar{e}+v
\end{equation}\)
then nucleus will have 2 protons and 1 neutron, i.e. triton atom converts in \(\begin{equation}
{ }_{2} \mathrm{He}^{3}
\end{equation}\) (2 proton and 1 neutron). Binding energy of \(\begin{equation}
{ }_{1} \mathrm{He}^{3}
\end{equation}\) is much smaller than \(\begin{equation}
{ }_{2} \mathrm{He}^{3}
\end{equation}\), so transformation is not possible energetically.
Nuclear Class 12 Chapter 13 MCQ Question 4.
Nuclear force is a ……….. and ……….. force.
(A) Strong, long – range
(B) Strong, short range
(C) Weak, long – range
(D) Weak, short – range
Answer:
(B) Strong, short range
Explanation:
Nudear force is the strongest short – range force which binds the neutrons and protons in a nudeus.
MCQ On Nuclei Class 12 Chapter 13 Question 5.
Two nuclei have mass number in the ratio 1 : 2. The ratio of their nudear densities is
(A) 1 : 2
(B) 2 : 1
(C) 1 : 1
(D) Cannot be defined from mass number ratio
Answer:
(C) 1 : 1
Explanation:
Nuclear density is same for all nuclei.
Question 6.
The mass of a nucleus in its ground state is
(A) less than the total mass of neutrons and protons.
(B) greater than the total mass of neutrons and protons.
(C) equal to the total mass of neutrons and protons.
(D) equal to the total mass of neutron, protons and electrons.
Answer:
(A) less than the total mass of neutrons and protons.
Explanation:
Protons and neutrons have to come very dose to form a nucleus. In order to achieve this doseness, a lot of energy is required. This energy is provided by the nucleons at the expense of certain portion of their masses. For this reason, the mass of a nucleus in its ground state is always less than the total mass of the constituent neutrons and protons.
Question 7.
……….. has the mass closest to the mass of positron.
(A) Proton
(B) Neutron
(C) Electron
(D) Neutrino
Answer:
(C) Electron
Explanation:
Positron is anti – particle of electron.
Question 8.
X amount of energy is required to remove an electron from its orbit and Y amount of energy is required to remove a nucleon from the nucleus.
(A) X = Y
(B) X > Y
(C) Y > X
(D) X ≥ Y
Answer:
(C) Y > X
Explanation:
Nuclear force is greater than Coulomb force.
Question 9.
Suppose we consider a large number of containers each containing initially 10,000 atoms of a radio – active material with a half-life of 1 year. After 1 year,
(A) all the containers will have 5,000 atoms of the material.
(B) all the containers will contain the same number of atoms of the material but that number will only be approximately 5,000.
(C) the containers will in general have different numbers of the atoms of the material but their average will be close to 5,000.
(D)none of the containers can have more than 5000 atoms.
Answer:
(C) the containers will in general have different numbers of the atoms of the material but their average will be close to 5,000.
Explanation:
Half – life time for a radio – active substance is defined as the time in which a radio – active atomic substance remains half of its original value of radio – active atom. Given that, Half – life = 1 year. So, after 1 year means one half – life, that is, average atoms of radioactive substance remain after 1 year in each container is equal to half of 10,0d0 = 5,000 atoms (average).
Question 10.
Consider the following reaction:
\(\begin{equation}{ }_{Z}^{A} X \rightarrow{ }_{Z+1}^{A} Y \rightarrow{ }_{Z-1}^{A-4} Z \rightarrow{ }_{Z-1}^{A-4} Z
\end{equation}\)
Radioactive radiation emitted in the following sequence:
(A) β, α, γ
(B) α, β, γ
(C) γ, β, α
(D) β, γ, α
Answer:
(A) β, α, γ
Explanation:
In β – emission, A remains same and Z increases by 1.
In α – emission, A decreases by 4 and Z decreases by 2.
In γ – emission, there is no change in A and Z.
Question 11.
Which of the following material will be the best moderator for a nuclear power plant ?
(A) Lighter element
(B) Heavier element
(C) Both of the above
(D) None of the above
Answer:
(A) Lighter element
Explanation:
Neutron will be slowed down more if the size of moderator atom is doser to a neutron. For this reason, lighter element will be more efficient moderator.
Assertion And Reason Based MCQs (1 Mark each)
Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is NOT the correct explanation of A
(C) A is true but R is false
(D) A is false and R is true
Question 1.
Assertion (A): Two atoms of different elements having same mass number but different atomic numbers are called isobars.
Reason (R): Atomic number is the number of protons present and atomic number is the total number of protons and neutrons present in a nucleus.
Answer:
(B) Both A and R are true but R is NOT the correct explanation of A
Explanation:
Two atoms of different elements having same mass number but different atomic numbers are called isobars. The assertion is true. Atomic number is the number of protons present and atomic number is the total number of protons and neutrons present in a nucleus. The reason is also true. But the reason does not explain the assertion.
Question 2.
Assertion (A): Nuclear force is same between neutron – neutron, proton – proton and neutron – proton.
Reason (R): Nuclear force is charge independent.
Answer:
(A) Both A and R are true and R is the correct explanation of A
Explanation:
Nuclear force acts between nucleons. It is a powerful attractive force and acts in a very short distance.
Neutrons are electrically neutral. So, neutron – neutron is neither attractive nor repulsive force acting. So, Nuclear force binds them together. Protons are having +e charge each. They experience a repulsive force. But for the short distance, the attractive nuclear force is strong enough to overcome this force. So, assertion and reason both are true and the reason explains the assertion.
Question 3.
Assertion (A): Electrons do not experience strong nuclear force.
Reason (R): Strong nuclear force is charge independent.
Answer:
(B) Both A and R are true but R is NOT the correct explanation of A
Explanation:
Nuclear force is a powerful attractive force acts as long as the distance between particles is within \(\begin{equation}10^{-15} \mathrm{~m}\end{equation}\). This force is charge independent. But as distance increases, the effect of nuclear force rapidly falls.
Electrons are distributed far away. The distance is beyond the range of the nuclear force. Hence nuclear force has no effect on electrons. So, the assertion and reason both are true. But the reason does not explain the assertion.
Question 4.
Assertion (A): The binding energy per nucleon, for nuclei with mass number (A) > 56 decreases with A.
Reason (R): Nuclear force is weak in heavier nuclei.
Answer:
(C) A is true but R is false
Explanation:
From the binding energy per nucleon vs. mass number, we find that binding energy per nucleon is maximum at A = 56. After that, binding energy per nucleon decreases as A increases. So, assertion is true. Nuclear force remains same for all nuclei. Hence the reason is false.
Question 5.
Assertion (A): Density of all the nuclei is same.
Reason (R): Radius of nucleus is directly proportional to the cube root of mass number.
Answer:
Assertion (A): Density of all the nuclei is same.
Explanation:
Radius of nucleus = \(\begin{equation}
=\mathrm{R}=\mathrm{R}_{0} \mathrm{~A}^{1 / 3}
\end{equation}\)
So, Volume of nudeus, \(\begin{equation}
V=\frac{4}{3} \pi R_{0}^{3} A
\end{equation}\)
Considering mass of proton = mass of neutron = m
The mass of the nudeus = M = mA
So, density = \(\begin{equation}
\mathrm{M} / \mathrm{V}=\frac{m \mathrm{~A}}{\frac{4}{3} \pi \mathrm{R}_{0}^{3} \mathrm{~A}}=\frac{m}{\frac{4}{3} \pi \mathrm{R}_{0}^{3}}
\end{equation}\)
So, the mean density is independent of mass number.
So, assertion and reason both are true and the reason properly explains the assertion.
Case-Based MCQs
Attempt any 4 sub – parts out of 5. Each sub – part carries 1 mark.
I. Read the following text and answer the following questions on the basis of the same:
India’s atomic energy programme:
The atomic energy programme in India was launched around the time of independence under the leadership of Homi J. Bhabha (1909 – 1966). An early historic achievement was the design and construction of the first nuclear reactor in India (named Apsara) which went critical on August 4, 1956. India indigenously designed and constructed plutonium plant at Trombay, which ushered in the technology of fuel reprocessing (separating useful fissile and fertile nuclear materials from the spent fuel of a reactor).
Research reactors that have been subsequently commissioned include ZERLINA, PURNIMA (I, II and III), DHRUVA and KAMINI. KAMINI is the country’s first large research reactor that uses \(\begin{equation}
\text { U-233 }\end{equation}\) as fuel. The main objectives of the Indian Atomic Energy programme are to provide safe and reliable electric power for the country’s social and economic progress and to be self reliant in all aspects of nuclear technology.
Exploration of atomic minerals in India undertaken since the early fifties has indicated that India has limited reserves of uranium, but fairly abundant reserves of thorium. Accordingly, our country has adopted a three – stage strategy of nuclear power generation. The first stage involves the use of natural uranium as a fuel, with heavy water as moderator. The Plutonium – 239 obtained from reprocessing of the discharged fuel from the reactors then serves as a fuel for the second stage – the fast breeder reactors.
They are so called because they use fast neutrons for sustaining the chain reaction (hence no moderator is needed) and, besides generating power, also breed more fissile species (plutonium) than they consume. The third stage, most significant in the long term, involves using fast breeder reactors to produce fissile Uranium-233 from Thorium-232 and to build power reactors based on them.
Question 1.
India’s atomic energy programme was launched by:
(A) Shanti Swarup Bhatnagar
(B) Homi J. Bhabha
(C) Meghnad Saha
(D) Daulat Singh Kothari
Answer:
(B) Homi J. Bhabha
Explanation:
The atomic energy programme in India was launched around the time of independence under the leadership of Homi J. Bhabha (1909-1966).
Question 2.
First nuclear reactor of India :
(A) APSARA
(B) ZERLINA
(C) DHRUBA
(D) KAMINI
Answer:
(A) APSARA
Explanation: An early historic achievement was the design and construction of the first nuclear reactor in India named APSARA.
Question 3.
Which one of the following is not a nuclear reactor ?
(A) PURNIMA
(B) DHRUVA
(C) KAMINI
(D) ARYABHATTA
Answer:
(D) ARYABHATTA
Explanation:
ARYABHATTA is an Indian artificial satellite.
Question 4.
The main objectives of the Indian Atomic Energy programme:
(A) Development of Nuclear weapons for success in warfare
(B) Generation of safe and reliable electric power
(C) Efficient medical treatment
(D) To breed more fissile species
Answer:
(B) Generation of safe and reliable electric power
Explanation:
The main objectives of the Indian Atomic Energy programme are to provide safe and reliable electric power for the country’s social and economic progress and to be self – reliant in all aspects of nuclear technology.
Question 5.
India has limited reserves of ……….. but fairly abundant reserves of ……….. :
(A) Plutonium, Thorium
(B) Thorium, Uranium
(C) Plutonium, Uranium
(D) Uranium, Thorium
Answer :
(D) Uranium, Thorium
Explanation:
Exploration of atomic minerals in India undertaken since the early fifties has indicated that India has limited reserves of uranium, but fairly abundant reserves of thorium.
II. Read the following text and answer the following questions on the basis of the same:
Grand Unification Theory :
There are four fundamental forces in the universe :
- Gravitational force
- Electromagnetic force
- The weak nuclear force
- The strong nuclear force
The weak and strong forces are effective only over a very short range and dominate only at the level of subatomic particles. Gravitational force and Electromagnetic force have infinite range.
The Four Fundamental Forces and their strengths :
- Gravitational Force – Weakest force; but has infinite range.
- Weak Nuclear Force – Next weakest; but short range.
- Electromagnetic Force – Stronger, with infinite range.
- Strong Nuclear Force – Strongest; but short range.
Unification:
- The weak nuclear force and electromagnetic force have been unified under the Standard Electroweak Theory, (Glashow, Weinberg and Salaam were awarded the Nobel Prize for this in 1979).
- Grand unification theories attempt to treat both strong nuclear force and electroweak force under the same mathematical structure.
- Theories that add gravitational force to the mix and try to unify all four fundamental forces into a single force are called Superunified Theories. It has not yet been successful.
Question 1.
What are the 4 fundamental forces ?
(A) Gravitational force, electromagnetic force, nuclear force, Tension force
(B) Gravitational force, electromagnetic force, nuclear force, Frictional force
(C) Gravitational force, electromagnetic force, weak nuclear force, strong nuclear force
(D) Frictional force, electric force, nuclear force, magnetic force
Answer:
(C) Gravitational force, electromagnetic force, weak nuclear force, strong nuclear force
Explanation:
There are four fundamental forces in the universe:
- Gravitational force
- Electromagnetic force
- the weak nuclear force
- the strong nuclear force
Question 2.
Which fundamental force is always attractive ?
(A) Electric force
(B) Magnetic force
(C) Gravitational force
(D) Strong nuclear force
Answer :
(C) Gravitational force
Explanation:
Gravitational force is always attractive. There is no repulsive gravitational force.
Question 3.
Which two fundamental forces have been unified by Standard Electroweak Theory ?
(A) Weak nuclear force and electromagnetic force
(B) Strong nuclear force and electromagnetic force
(C) Gravitational force and electromagnetic force
(D) Weak nuclear force and strong nuclear force
Answer:
(A) Weak nuclear force and electromagnetic force
Explanation:
The weak nuclear force and electromagnetic force have been unified under the Standard Electroweak theory. For this, Glashow, Weinberg and Salaam were awarded the Nobel Prize in 1979.
Question 4.
Which one is the weakest force ?
(A) Weak nuclear force
(B) Electromagnetic force
(C) Strong magnetic force
(D) Gravitational force
Answer:
(D) Gravitational force
Explanation:
Gravitational force is the weakest force.
Question 5.
Which of the following forces have infinite ranges ?
(A) Weak nuclear force and strong nuclear force
(B) Gravitational force and Electromagnetic force
(C) Weak nuclear force and Gravitational force
(D) All the forces
Answer:
(B) Gravitational force and Electromagnetic force
Explanation:
Gravitational force and Electromagnetic force are extended upto infinity.