Half-lives of two radioactive substances A and B respectively are 20 min and 40 min.  Initially, the samples of A and B have an equal number of nuclei. After 80 min the ratio of the remaining number of A and B nuclei is:

1. 1 : 16

2. 4 : 1

3. 1 : 4 

4. 1 : 1

Subtopic:  Radioactivity (OLD NCERT) |
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Radioactive C2760o is transformed into stable N2860i by emitting two γ-rays of energies

1. 1.33 MeV and 1.17 MeV in succession

2. 1.17 MeV and 1.33 MeV in succession

3. 1.37 MeV and 1.13 MeV in succession

4. 1.17 MeV and 1.13 MeV in succession

Subtopic:  Radioactivity (OLD NCERT) |
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The volume occupied by an atom is greater than the volume of the nucleus by factor of about [2003]

1. 1010 

2. 1015 

3. 101 

4. 105

Subtopic:  Mass-Energy Equivalent |
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A radioactive nucleus undergoes a series of decay according to the scheme 

AαA1βA2αA3γA4

If the mass number and atomic number of A are 180 and 72 respectively, then what are these number for A4?

1. 172 and 69 

2. 174 and 70

3. 176 and 69

4. 176 and 70

Subtopic:  Types of Decay |
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What fraction of a radioactive material will get disintegrated in a period of two half-lives?

1. whole

2. half

3. one-fourth

4. three-fourth

Subtopic:  Radioactivity (OLD NCERT) |
 56%
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If the nucleus A1327l has a nuclear radius of about 3.6 fm, then T52125e would have its radius approximately as [2007]

1. 6.0 fm 

2. 9.6 fm

3. 12.0 fm 

4. 4.8 fm

Subtopic:  Nuclear Binding Energy |
 82%
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After two hours, one-sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is [Bihar MEE 1995; Manipal MEE 1995; MP PMT 1997; AFMC 2000, 05; DPMT 2002]

1. 15 minutes 

2. 30 minutes

3. 45 minutes

4. 1 hour

Subtopic:  Radioactivity (OLD NCERT) |
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PMT - 1997
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Atomic weight of boron is 10.81 and it has two isotopes B510 and B511. Then, the ratio of atoms of  B510 and B511 in nature would be 

1. 19 : 81

2. 10 : 11 

3. 15 : 16 

4. 81 : 19

Subtopic:  Mass-Energy Equivalent |
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The half-life of radium is 1600 yr.  The fraction of a sample of radium that would remain

after 6400 yr [1991]

1. 14   

2. 12 

3. 18 

4. 116

Subtopic:  Radioactivity (OLD NCERT) |
 81%
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The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life 30 min decreases to 5 s-1 after 2 h. The initial count rate was [1995]

1. 20 s-1 

2. 25 s-1 

3. 80 s-1 

4. 625 s-1

Subtopic:  Radioactivity (OLD NCERT) |
 69%
From NCERT
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