# Assertion Reason Physics Chapter 12 Atoms

Questions of Assertion Reason of Physics Chapter 12 Atoms CBSE Class 12 are very simple to understand as this chapter deals with Atoms. To solve assertion reason type questions of Physics, a deeper understanding of concept about Alpha-particle Scattering and Rutherford’s Nuclear Model of Atom, Atomic Spectra, Bohr Model of the Hydrogen Atom, The Line Spectra of the Hydrogen Atom and DE Broglie’s Explanation of Bohr’s Second Postulate of Quantisation 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 12 Atoms

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: The force of repulsion between atomic nucleus and α-particle varies with distance according to inverse square law.
Reason: Rutherford did α-particle scattering experiment.

Ans.1. (b)
Rutherford confirmed that the repulsive force of α- particle due to nucleus varies with distance according to inverse square law and that the positive charges are concentrated at the centre and not distributed throughout the atom.

Question.2.
Assertion: According to classical theory the proposed path of an electron in Rutherford atom model will be parabolic.
Reason: According to electromagnetic theory an accelerated particle continuously emits radiation.

Ans.2. (d)
According to classical electromagnetic theory, an accelerated charged particle continuously emits radiation. As electrons revolving in circular paths are constantly experiencing centripetal acceleration, hence they will be losing their energy continuously and the orbital radius will go on decreasing, form spiral and finally the electron will fall in the nucleus.

Question.3.
Assertion: Bohr had to postulate that the electrons in stationary orbits around the nucleus do not radiate.
Reason: According to classical physics all moving electrons radiate.

Ans.3. (b)
Bohr postulated that electrons in stationary orbits around the nucleus do not radiate. This is the one of Bohr’s postulate, According to this the moving electrons radiates only when they go from one orbit to the next lower orbit.

Question.4.
Assertion: Electrons in the atom are held due to coulomb forces.
Reason: The atom is stable only because the centripetal force due to Coulomb’s law is balanced by the centrifugal force.

Ans.4. (c)
According to postulates of Bohr’s atom model the electron revolves around the nucleus in fixed orbit of definite radii. As long as the electron is in a certain orbit it does not radiate any energy.

Question.5.
Assertion: Hydrogen atom consists of only one electron but its emission spectrum has many lines.
Reason: Only Lyman series is found in the absorption spectrum of hydrogen atom whereas in the emission spectrum, all the series are found.

Ans.5. (b)
When the atom gets appropriate energy from outside, then this electron rises to some higher energy level. Now it can return either directly to the lower energy level or come to the lowest energy level after passing through other lower energy levels hence all possible transitions take place in the source and many lines are seen in the spectrum.

Question.6.
Assertion: Between any two given energy levels, the number of absorption transitions is always less than the number of emission transitions.
Reason: Absorption transitions start from the lowest energy level only and may end at any higher energy level. But emission transitions may start from any higher energy level and end at any energy level below it.

Ans.6. (a)
Both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

Question.7.
Assertion: In Lyman series, the ratio of minimum and maximum wavelength is 3/4
Reason: Lyman series constitute spectral lines corresponding to transition from higher energy to ground state of hydrogen atom.

Ans.7. (b) Both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.