A certain mass of hydrogen is changed to helium by the process of

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 Multiple Choice QuestionsMultiple Choice Questions

321.

Two radioactive substances A and B have decay constants 5 λ and λ respectively. At t = 0, they have the same number of nuclei. The ratio of number of nuclei of A to that of B will be (1/e)2 after a time interval of

  • 1λ

  • 12λ

  • 13λ

  • 14λ


322.

The half-life of a radioactive isotope X is 20 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio 1 : 7 in a sample of a given rock. The age of the rock is estimated to be

  • 40 yr

  • 60 yr

  • 80 yr

  • 100 yr


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323.

A certain mass of hydrogen is changed to helium by the process of fusion. The mass defect in fusion reaction is 0.02866 u. The energy liberated per u is (given 1 u = 931 MeV)

  • 2.67 MeV

  • 26.7 MeV

  • 6.675 MeV

  • 13.35 MeV


C.

6.675 MeV

Here, Δm = 0.02866 U

 Energy liberated = 0.02866 × 9314 = 26.74                               = 6.675 MeV


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324.

For the radioactive nuclei that undergo either α or β decay, which one of the following cannot occur ?

  • Isobar of original nucleus is produced

  • Isotope of the original nucleus is produced

  • Nuclei with higher atomic number than that of the original nucleus is produced

  • Nuclei with lower atomic number than that of the original nucleus is produced


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