If a radioactive substance reduces to 116 of its original mass in 40 days, what is its half-life 

(1) 10 days           

(2) 20 days

(3) 40 days           

(4) None of these

Subtopic:  Radioactivity (OLD NCERT) |
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A radioactive nucleus with Z protons and N neutrons emits an α-particle, 2β-particles and 2 gamma rays. The number of protons and neutrons in the nucleus left after the decay respectively, are 

(1) Z – 3, N – 1                 

(2) Z – 2, N – 2

(3) Z – 1, N – 3                 

(4) Z, N – 4

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99% of a radioactive element will decay between

(1) 6 and 7 half lives             

(2) 7 and 8 half lives

(3) 8 and 9 half lives             

(4) 9 half lives

Subtopic:  Radioactivity (OLD NCERT) |
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The half-life of a radioactive substance against α-decay is 1.2×107 s. What is the decay rate for 4×1015 atoms of the substance

(1) 4.6×1012 atoms/s         

(2) 2.3×1011 atoms/s

(3) 4.6×1010 atoms/s          

(4) 2.3×108 atoms/s

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In a sample of radioactive material, what percentage of the initial number of active nuclei will decay during one mean life 

(1) 69.3%           

(2) 63%

(3) 50%               

(4) 37%

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The S.I. unit of radioactivity is 

(1) Roentgen         

(2) Rutherford

(3) Curie               

(4) Becqueral

Subtopic:  Radioactivity (OLD NCERT) |
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A radioactive material has an initial amount 16 gm. After 120 days it reduces to 1 gm, then the half-life of radioactive material is 

(1) 60 days             

(2) 30 days

(3) 40 days             

(4) 240 days

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The activity of a sample of a radioactive material is A1, at time t1 and A2 at time t2 (t2>t1). If its mean life T, then 

(1) A1t1=A2t2           

(2) A1-A2=t2-t1
(3) A2=A1et1-t2/T   

(4) A2=A1et1/t2T

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Nucleus produced due to α-decay of the nucleus XZA is

(1) YZ+2A+4                     

(2) YZA

(3) YZ-2A-4                    

(4) YZ-4A-2

Subtopic:  Types of Decay |
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Which of the following processes represents a gamma-decay

(1) XZA+γXZ-1A+a+b 

(2) XZA+n01XZ-2A-3+c

(3) XZAXZA+f

(4) XZA+e-1  XZ-1A+g

Subtopic:  Types of Decay |
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