Atoms And Nuclei JEE Mains Questions - List Of Most Asked Questions With Solutions

NTA will shortly release the JEE Main Syllabus 2025 at jeemain.nta.ac.in. Last Year, the complete syllabus of JEE Main underwent some major changes. According to the latest syllabus guidelines, the weightage of Physics has dropped to 22.5%. Due to these changes in the syllabus, certain shifts in chapter-wise weightage have been observed. Atoms and Nuclei are among such topics. It’s among the least weightage topics in JEE Main Physics Syllabus 2025. This chapter holds 1.39% weightage in the whole syllabus.

• Atoms and Nuclei is a part of the General Physics section, and every year around 2-3 questions are asked from this chapter. Due to the drop in weightage, you can expect 1-2 questions in JEE Main 2025.
• Atoms and Nuclei in JEE Mains Physics Syllabus 2025 covers all the basic concepts on units and measurements, fundamentals of units, dimensions etc.

Aspirants consider Atoms and Nuclei as one of the Easiest Chapters in Physics for JEE Main 2025. Even though this chapter has the least weightage in the syllabus, to develop a strong foundation in physics, this particular chapter plays a pivotal role. Hence the candidates need to develop a clear understanding of this chapter. The list of most asked questions from this chapter will help the students with their preparation.

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Some of the most important topics for the JEE Main exam in the area of atoms and nuclei include:

• Bohr's model of the atom
• Hydrogen spectrum
• Quantum numbers
• Electronic configuration
• Pauli exclusion principle
• Aufbau principle and Hund's rule
• Isotopes and isobars
• Radioactivity
• Nuclear reactions
• Binding energy

Atoms and Nuclei JEE Mains Questions -

List Of Most Asked Questions With Solutions

In the (JEE) Main, the topic of Physics and Measurement often features questions that have appeared multiple times in previous years. Many questions in this section are either repeated or follow similar patterns, with only minor changes, such as different numerical values or slight modifications in wording.Certain questions have been repeated as many as five times.

Here are some of the most frequently asked and repeated questions:

Question 1 :

The atomic structure section is a scoring topic in the JEE Main exam, with a weightage of around 6-8%. This means that students can expect 3-4 questions from this chapter in the exam.

1. The number of protons in the nucleus of an atom is called its:

   A) Atomic number

   B) Mass number

   C) Neutron number

   D) Isotopic number

Solution:

Option A is correct. The number of protons in the nucleus of an atom is called its atomic number.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. In a nuclear reaction, which of the following quantities is always conserved?

   A) Mass

   B) Number of nucleons

   C) Charge

   D) All of the above

Solution:

Option D is correct. In a nuclear reaction, mass, the number of nucleons, and charge are conserved.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. Which of the following is true for a radioactive substance undergoing α-decay?

   A) Its atomic number increases by 2

   B) Its atomic number decreases by 2

   C) Its mass number increases by 4

   D) Its mass number decreases by 2

Solution:

Option B is correct. During α-decay, the atomic number of the element decreases by 2 and the mass number decreases by 4.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. The half-life of a radioactive element is 10 years. How much of the element will remain after 30 years?

   A) 1/8

   B) 1/4

   C) 1/2

   D) None

Solution:

Option A is correct. After 30 years (3 half-lives), the remaining quantity will be (1/2)³ = 1/8 of the original amount.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. Which particle is emitted in the β-decay of a neutron?

   A) Proton

   B) Electron

   C) Neutron

   D) Photon

Solution:

Option B is correct. In β-decay, a neutron decays into a proton, and an electron (β-particle) is emitted.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. What is the energy released in the fission of one nucleus of Uranium-235?

   A) 200 MeV

   B) 2.5 MeV

   C) 25 MeV

   D) 250 MeV

Solution:

Option A is correct. The energy released in the fission of one Uranium-235 nucleus is approximately 200 MeV.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. Which of the following elements is not radioactive?

   A) Uranium

   B) Radon

   C) Thorium

   D) Calcium

Solution:

Option D is correct. Calcium is not a radioactive element, while Uranium, Radon, and Thorium are.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. The activity of a radioactive substance is measured to be 500 disintegrations per second. After 5 hours, the activity is reduced to 250 disintegrations per second. The half-life of the substance is:

   A) 2 hours

   B) 5 hours

   C) 10 hours

   D) 20 hours

Solution:

Option B is correct. Since the activity is halved after 5 hours, the half-life of the substance is 5 hours.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. The binding energy per nucleon of deuterium is 1.1 MeV. What is the total binding energy of a deuterium nucleus?

   A) 1.1 MeV

   B) 2.2 MeV

   C) 3.3 MeV

   D) 4.4 MeV

Solution:

Option B is correct. A deuterium nucleus has 2 nucleons, so the total binding energy is 2 * 1.1 MeV = 2.2 MeV.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.

1. Which of the following is responsible for holding the protons and neutrons together in a nucleus?

   A) Gravitational force

   B) Electromagnetic force

   C) Nuclear force

   D) Weak force

Solution:

Option C is correct. The nuclear force is responsible for holding protons and neutrons together in the nucleus.

This question has been asked thrice - 30-Jan-2024 Shift 2, JEE Main 2020, JEE Main 2016.