Alpha particles are 

1. 2 free protons

2. helium atoms

3. singly ionized helium atoms

4. doubly ionised helium atoms

Subtopic:  Radioactivity (OLD NCERT) |
 61%
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A radioactive sample with a half-life of 1 month has the label: 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier? 

1. 1.0 microcurie       

2. 0.5 microcurie           

3. 4 microcurie             

4. 8 microcurie

Subtopic:  Radioactivity (OLD NCERT) |
 54%
From NCERT
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If the nuclear force between two protons, two neutrons and between a proton and a neutron is denoted by \(F_{pp} ,F_{nn}\) and \(F_{pn}\) respectively, then:
1. \(F_{p p} \approx F_{n n} \approx F_{p n}\)
2. \(F_{p p} \neq F_{n n}\) and \(F_{p n} = F_{n n}\)
3. \(F_{p p} = F_{n n} = F_{p n}\)
4. \(F_{p p} \neq F_{n n} \neq F_{p n}\)
Subtopic:  Nuclear Energy |
From NCERT
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A radioactive element has half-life period 800 yr. After 6400 yr, what fraction will remain? [1989]

1. 12

2. 116 

3. 18 

4.1256

Subtopic:  Radioactivity (OLD NCERT) |
 77%
From NCERT
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If a proton and anti-proton come close to each other and annihilate, how much energy will be released:

1. 1.5×10-10 J           

2. 3×10-10 J         

3. 4.5×10-10 J         

4. None of these

Subtopic:  Mass-Energy Equivalent |
From NCERT
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The stable nucleus that has a radius half of the radius of \(\mathrm{Fe}^{56}\) is:
1. \(\mathrm{Li}^7\)
2. \(\mathrm{Na}^{21}\)
3. \(\mathrm{S}^{16}\)
4. \(\mathrm{Ca}^{40}\)

Subtopic:  Nucleus |
 66%
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The mass density of a nucleus varies with mass number A as [1992]

1. A2

2. A 

3. Constant 

4. 1A

Subtopic:  Nuclear Binding Energy |
 78%
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Energy released in the fission of a single U23592 nucleus is 200 MeV. The fission rate of a U23592 filled reactor operating at a power level of 5 W is 

1. 1.56×10-10 s-1 

2. 1.56×1011 s-1

3. 1.56×10-16 s-1   

4. 1.56×10-17 s-1

Subtopic:  Nuclear Energy |
 70%
From NCERT
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In one \(\alpha \text-\) and \(2\beta \text-\)emissions:

1. mass number reduced by \(2\)
2. mass number reduces by \(6\)
3. atomic number is reduced by \(2\)
4. atomic number remains unchanged

Subtopic:  Types of Decay |
 78%
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Which of the following is used as a moderator in nuclear reactors? 

1. Plutonium 

2. Cadmium 

3. Heavy water

4. Uranium 

Subtopic:  Nuclear Energy |
 80%
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