10 g of radioactive material of half-life 15 year is kept in store for 20 years. The disintegrated material mass is 

1. 12.5 g

2. 10.5 g

3. 6.03 g

4. 4.03 g

Subtopic:  Radioactivity (OLD NCERT) |
 57%
From NCERT
PMT - 2002
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If a radioactive nucleus decays according to the following reaction

X18072αX1βX2αX3γX4

then the mass number and the atomic number of X4 then the mass number and the atomic number of X4 will be, respectively 

1. 172, 70 

2. 172, 69

3. 172, 68

4. 171, 69

Subtopic:  Types of Decay |
 86%
From NCERT
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A radioactive material has mean-lives of 1620 yr and 520 yr for α and β-emission. The material decays by simultaneous α and β-emission. The time in which 1/4th of the material remains intact is 

1. 4675 yr 

2. 720 yr

3. 545 yr 

4. 324 yr

Subtopic:  Radioactivity (OLD NCERT) |
From NCERT
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The radioactivity of an element becomes 164th of its original value in 60 seconds. Then the half value period is

1. 5 sec 

2. 10 sec 

3. 20 sec

4. 30 sec

Subtopic:  Radioactivity (OLD NCERT) |
 91%
From NCERT
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A nucleus of P84210o originally at rest emits α particle with speed ν. What will be the recoil speed of the daughter necleus. 

1. 4ν / 206

2. 4ν / 214

3. ν / 206 

4. ν / 214

Subtopic:  Types of Decay |
 75%
From NCERT
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An atom of mass number 15 and atomic number 7 captures an α-particle and then emits a proton. The mass number and atomic number of the resulting product will respectively be

1. 14 and 2

2. 15 and 3

3. 16 and 4 

4. 18 and 8

Subtopic:  Types of Decay |
 78%
From NCERT
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The wavelength of Kα X-rays for lead isotopes Pb208, Pb206, Pb204 are λ1, λ2 and λ3 respectively. Then

1. λ1=λ2>λ3   

2. λ1>λ2>λ3

3. λ1<λ2<λ3 

4. λ2=λ1=λ3

Subtopic:  X-Ray (OLD NCERT) |
 57%
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Solar energy is mainly caused due to 

1. fusion of protons during synthesis of heavier elements

2. gravitational contraction

3. burning of hydrogen in the oxygen

4. fission of uranium present in the sun

Subtopic:  Mass-Energy Equivalent |
 82%
From NCERT
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A sample of radioactive elements contains 4×1010 active nuclei. If half-life of element is 10 days, then the number of decayed nuclei after 30 days is 

1. 0.5×1010   

2. 2×1010

3. 3.5×1010

4. 1×1010

Subtopic:  Radioactivity (OLD NCERT) |
 54%
From NCERT
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A and B are two radioactive substances whose half-lives are 1 and 2 years respectively. Initially 10 g of A and 1 g of B is taken. The time (approximate) after which they will have the same quantity remaining is:

1. 6.62 yr

2. 5 yr   

3. 3.2 yr 

4. 7 yr

Subtopic:  Radioactivity (OLD NCERT) |
 58%
From NCERT
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