If half life of a radioactive element is 3 hours, after 9 hours its activity becomes 

(1) 1/9                     

(2) 1/27

(3) 1/6                     

(4) 1/8

Subtopic:  Radioactivity (OLD NCERT) |
 80%
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At any instant the ratio of the amount of radioactive substances is 2 : 1. If their half lives be respectively 12 and 16 hours, then after two days, what will be the ratio of the substances?

(1) 1 : 1                 

(2) 2 : 1

(3) 1 : 2                 

(4) 1 : 4

Subtopic:  Radioactivity (OLD NCERT) |
 66%
From NCERT
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Which of the following isotopes is used for the treatment of cancer 

(1) K40        

(2) Co60

(3) Sr90       

(4) I131

Subtopic:  Radioactivity (OLD NCERT) |
 61%
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If half-life of a radioactive atom is 2.3 days, then its decay constant would be 

(1) 0.1           

(2) 0.2

(3) 0.3           

(4) 2.3

Subtopic:  Radioactivity (OLD NCERT) |
 81%
From NCERT
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A radio isotope has a half life of 75 years. The fraction of the atoms of this material that would decay in 150 years will be

(1) 66.6%               

(2) 85.5%

(3) 62.5%               

(4) 75%

Subtopic:  Radioactivity (OLD NCERT) |
 82%
From NCERT
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An artificial radioactive decay series begins with unstable Pu94241. The stable nuclide obtained after eight α decays and five β-decays is 

(1) Bi83209         

(2) Pb82209

(3) Ti82205         

(4) Hg82201

Subtopic:  Radioactivity (OLD NCERT) |
 80%
From NCERT
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The activity of a sample is 64×10-5 Ci. Its half-life is 3 days. The activity will become 5×10-6 Ci after 

(1) 12 days         

(2) 7 days

(3) 18 days         

(4) 21 days

Subtopic:  Radioactivity (OLD NCERT) |
 67%
From NCERT
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The half-life of radon is 3.8 days. Three forth of a radon sample decay in

(1) 5.02 days         

(2) 15.2 days

(3) 7.6 days           

(4) 11.4 days

Subtopic:  Radioactivity (OLD NCERT) |
 83%
From NCERT
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A nucleus of an element X84202 emits an α-particle first, a β-particle next and then a gamma photon. The final nucleus formed has an atomic number 

(1) 200           

(2) 199

(3) 83             

(4) 198

Subtopic:  Types of Decay |
 78%
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Plutonium decays with a half-life of 24000 years. If the plutonium is stored for 72000 years, then the fraction of plutonium that remains is 

(1) 12          

(2) 13
(3) 14          

(4) 18

Subtopic:  Radioactivity (OLD NCERT) |
 82%
From NCERT
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