NCERT Solutions for Class 12 Physics Chapter 13 – Nuclei

NCERT Solutions for Class 12 Physics Chapter 13 – Nuclei are important to revise the chapter thoroughly. This chapter includes topics like alpha, beta and gamma decay, radioactivity, atomic mass, isotopes etc. There are 31 questions in this chapter that include reasoning questions, short answer questions, simple formula questions, analytical questions, observational questions and numerical problems. 

The best physics experts at Instasolv have prepared the NCERT Solutions for Class 12 Physics Chapter 13 for you. With the help of these solutions, you can understand the whole chapter quickly and ensure that you are fully prepared for CBSE exams.  We have provided step by step explanations of the chapter through these solutions.

Important Topics of NCERT Solutions for Class 12 Physics Chapter 13 – Nuclei

Atomic Mass 

CBSE Class 12 Physics NCERT Chapter 13 deals with the concept of the atomic mass of different elements. The atomic mass of different elements is expressed as atomic mass units that are near to the integral multiples of the mass of a hydrogen atom. 

A spectrometer is used for the accurate measurement of atomic masses and ikt is these accurate and exact measurements which reveal the existence of different kinds of atoms of the same element. 

These are similar in their chemical properties but they have different atomic mass. And this category of atoms with different atomic masses but the similar chemical property is termed as isotopes. 

Neutron and Nucleus 

A free neutron is different from a free proton, mainly because it is unstable and it decays into becoming a proton, an electron and an antineutrino. It has a mean life of about thousands and even though it is unstable unlike a proton, it remains in a stable state inside a nucleus. A nucleus has the following composition –

  • Z – it is the atomic number and is equal to the number of protons 
  • N – neutron number and is equal to the number of neutrons
  • A – mass number and is equal to the number of protons and the number of neutrons


You will learn in this chapter about a nuclear phenomenon where an unstable nucleus undergoes decay and this decay is termed to be radioactive decay. There are three major kinds of radioactive decay, and these are as follows –

  • α  – Decay – in case of alpha decay of an atom, a helium nucleus is emitted 
  • β – Decay – in case of beta decay of an atom, electrons or positrons are emitted
  • γ – Decay – in case of gamma decay of an atom, photons with a very high energy level are omitted

Exercise Discussion of NCERT Solutions for Class 12 Chapter 13 – Nuclei

  • The first question of NCERT Solutions for Class 12 Physics Chapter 13 is about finding the atomic mass of lithium-based on the value of the isotopes which has been given to you. In the second part of the same question, similar information has been given for Boron and you are required to find the abundance in this case. 
  • Exercise 13.2 and 13.3 are also similar in terms of mass extraction based on the provided values. These questions can play an important role in helping you fetch more marks in your CBSE exams.
  • Further, there are questions like 3.4, which might seem a bit lengthy in terms of calculations and working. Here you are needed to find the binding energy of the nuclei of Fe and Bi on the basis of the information given in the question. 
  • Question 13.5 also belongs to the category of lengthy questions and here you are asked to find the nuclear energy which will be required to separate all the neutrons and the protons from each other. You will have to use the Avagadro’s number and the equation of mass and energy to obtain your answer to this question. 
  • The chapter also has questions like 13.15 where you need to write down the nuclear reactions of the elements on the basis of the data that has been provided to you.
  • Question 13.22 is also similar and you are required to write the nuclear reactions for them and find their Q – value.

Benefits of NCERT Solutions for Class 12 Physics Chapter 13 – Nuclei

NCERT Solutions for Class 12 Physics Chapter 13 form the basis of the topic Nuclei. Solving the NCERT exercises is the best way to ensure that you are aware of the concepts of the chapter and are prepared for CBSE exams. This chapter will also provide you with fundamental knowledge for JEE and NEET tests. We have designed superior quality solutions for your better understanding.