Assertion Reason Physics Chapter 13 Nuclei

Questions of Assertion Reason of Physics Chapter 13 Nuclei CBSE Class 12 are very simple to understand as this chapter deals with Nuclei. To solve assertion reason type questions of Physics, a deeper understanding of concept about Atomic Masses and Composition of Nucleus, Size of the Nucleus, Mass-Energy and Nuclear Binding Energy, Nuclear Force, Radioactivity and Nuclear Energy is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.

How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.

How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.

In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:

Assertion (A)Reason (R)MCQ Options (Fixed for all questions)
If TrueTrue(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
If TrueTrue(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
If TrueFalse(c) Assertion (A) is true but reason (R) is false.
If FalseTrue(d) Assertion (A) is false but reason (R) is true.
If FalseFalse(e) Both Assertion and Reason are false.

Now, lets practice some Assertion Reason Questions of Physics: Chapter 13 Nuclei

For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.

Question.1.
Assertion: Density of all the nuclei is same.
Reason: Radius of nucleus is directly proportional to the cube root of mass number.

Ans.1. (a)
Both Assertion and Reason are correct and the Reason is a correct explanation
of the Assertion.

Question.2.
Assertion: Neutrons penetrate matter more readily as compared to protons.
Reason: Neutrons are slightly more massive than protons.

Ans.2. (b)
Both statements are separately correct.

Question.3.
Assertion: The mass number of a nucleus is always less than its atomic number.
Reason: Mass number of a nucleus may be equal to its atomic number.

Ans.3. (d)
In case of hydrogen atom mass number and atomic number are equal.

Question.4.
Assertion: The binding energy per nucleon, for nuclei with atomic mass number A > 100, decrease with A.
Reason: The forces are weak for heavier nuclei.

Ans.4. (c)
Nuclear force is nearly same for all nucleus.

Question.5.
Assertion: Radioactivity of 108 undecayed radioactive nuclei of half life of 50 days is equal to that of 1.2 x 108 number of undecayed nuclei of some other material with half life of 60 days.
Reason: Radioactivity is proportional to half-life.

Ans.5. (c)
The Assertion is correct but Reason is incorrect.

Question.6.
Assertion: The ionising power of β-particle is less compared to β-particles but their penetrating power is more.
Reason: The mass of β-particle is less than the mass of α- particle.

Ans.6. (b)
β-particles, being emitted with very high speed compared to α-particles, pass for very little time near the atoms of the medium. So the probability of the atoms being ionised is comparatively less. But due to this reason, their loss of energy is very slow and they can penetrate the medium through a sufficient depth.

Question.7.
Assertion: Radioactive nuclei emit \beta^{-1} particles.
Reason: Electrons exist inside the nucleus.

Ans.7. (c)
Electrons are not inside nucleus.

Question.8.
Assertion: _{Z}X^{A} undergoes 2 \alpha , 2 \beta -particles and 2\gamma -rays, the daughter product is _{Z-2}Y^{A-8} .
Reason: In α-decay the mass number decreases by 4 and atomic number decreases by 2. In β-decay the mass number remains unchanged, but atomic number increases by 1.

Ans.8. (a)
Both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

Question.9.
Assertion: The heavier nuclei tend to have larger N/Z ratio because neutron does not exert electric force.
Reason: Coulomb forces have longer range compared to the nuclear force.

Ans.9. (a)
Both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

Question.10.
Assertion: A free neutron decays to a proton but a free proton does not decay to a neutron. This is because neutron is an uncharged particle and proton is a charged particle.
Reason: Neutron has larger rest mass than the proton.

Ans.10. (d)
Both the Assertion and Reason are incorrect.

Question.11.
Assertion: Cobalt-60 is useful in cancer therapy.
Reason: Cobalt -60 is source of γ- radiations capable of killing cancerous cells.

Ans.11. (d)
Both the Assertion and Reason are incorrect.

Question.12.
Assertion: It is not possible to use ^{35}Cl as the fuel for fusion energy.
Reason: The binding energy of ^{35}Cl is to small.

Ans.12. (c)
The Assertion is correct but Reason is incorrect.

Question.13.
Assertion: Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.
Reason: For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei it decreases with increasing Z.

Ans.13. (d)
We know that energy is released when heavy nuclei undergo fission or light nuclei undergo fusion. Therefore statement (1) is correct. The second statement is false because for heavy nuclei the binding energy per nucleon decreases with increasing Z and for light nuclei, B.E/nucleon increases with increasing Z.