CBSE Class 12th Chapter, **Nuclei**** **comes under the topic Atoms & Nuclei which carries **6 Marks **in board exam. Experts of **Jagranjosh.com** offer the best practice material that covers all important questions so that students will not miss any portion while preparing for board exams or competitive exams. Consider the mentioned terms/questions at the time of studying.

- Define 1a.m.u? What is its relation with kilogram?
- Differentiate between isotones and isobars?
- If the radius of the earth is given 6,371 km. What would be the mass of earth?

(Given: R_{0 }= 1.2 x 10^{--15})

- Calculate the energy contained in 1kg of potatoes?
- Define mass defect and binding energy of nucleus? With binding energy curve in mind, show that why is uranium so unstable?
- What do you mean by the saturation property of nuclear forces?

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**GUESS PAPERS, Click Here**

- What do you understand by the term fission and fusion?
- The activity of a radioactive material drops to 1/14 th of its value in 24 hours. Calculate the half-life and the decay constant?
- Is the mass electrons obtained by all sources equal?
- The mass of β-particle is higher than the mass of electrons obtained by other sources, whereas β-particles are also electrons. Why?

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**PRACTICE PAPERS, Click Here**

- What do you mean by the half life of a radioactive element? Explain half life time and decay constant by drawing a curve between undisintegrated atoms of the element and time?
- After a certain apse of time, the fraction of radioactive polonium undecayed is found to be 4.625% of its initial quantity. What is the duration of this time lapse if the half life of polonium is 138 days?
- How can you show that the nuclear force is very much stronger than Coulomb force?
- What are the types of nuclear decay occurring in nature?
- What is activity of a radioactive simple? How can you account for the exponential decay of a radioactive species?

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**QUESTION PAPERS, Click Here**

- Differentiate between the units Becquerel and curie?
- Explain how radioactive elements can emit β-particles even though atomic nuclei do not contain these particles. Hence explain why the mass number of a radioactive nuclide does not change during β-decay?
- A radioactive sample is kept at the centre of a large evacuated sphere. How safe will it be?
- Why is the mass of nucleus always less than the sum of the masses of its constituents, neutrons and protons?
- Name the radiation which when becomes neutral, becomes the atom of a rare gas?
- Draw a graph showing the variation of potential energy of a pair of nucleons as a pair of nucleons as a function of their separation. Indicate the regions in which the nuclear force is attractive and repulsive?

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**NCERT SOLUTIONS, Click Here**

- Prove that the instantaneous rate of change of the activity of a radioactive substance is inversely proportional to the square of its half life?
- If the total number of protons and neutrons in a nuclear reaction is conserved, how then is the energy absorbed or evolved in the reaction? Explain.
- State the law of radioactive decay. If N
_{0}is the number of radioactive nuclei in the sample at some initial time t_{0}, find out the relation to determine the number N present at a subsequent time. Draw a plot of N as a function of time? - The half life of a given radioactive nuclide is 1338.6 days. What is the mean life of this nuclide? After how much time will a given sample of this radioactive nuclide get reduced to only 12.5% of its initial value?
- A star converts all its hydrogen to helium achieving 100% helium composition. It then converts helium to carbon via the reaction:

3_{2}^{4}He → _{2}^{12}C + 7.27 MeV

The mass of the star is 5.0 x 10^{30} kg and it generates energy at the rate of 5 x 10^{30} watt. How long will it take to convert all its helium to carbon?

- The half life of
_{6}^{12}C is 5700 years. What does it mean? Two radioactive nuclei P and Q initially contain an equal number of atoms. Their half life is 1 hour and 2 hours respectively. Calculate the ratio of their rates of disintegration after two hours?

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