If a radioactive substance reduces to 116 of its original mass in 40 days, what is its half-life 
(a) 10 days            (b) 20 days
(c) 40 days            (d) None of these

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Radioactivity
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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 
(a) Z – 3, N – 1                  (b) Z – 2, N – 2
(c) Z – 1, N – 3                  (d) Z, N – 4

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Radioactivity
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99% of a radioactive element will decay between

(a) 6 and 7 half lives             (b) 7 and 8 half lives
(c) 8 and 9 half lives             (d) 9 half lives

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Radioactivity
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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
(a) 4.6×1012 atoms/s          (b) 2.3×1011 atoms/s
(c) 4.6×1010 atoms/s          (d) 2.3×108 atoms/s

Concept Questions :-

Radioactivity
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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 
(a) 69.3%            (b) 63%
(c) 50%               (d) 37%

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Radioactivity
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The S.I. unit of radioactivity is 
(a) Roentgen          (b) Rutherford
(c) Curie                (d) Becqueral

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Radioactivity
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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 
(a) 60 days              (b) 30 days
(c) 40 days              (d) 240 days

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Radioactivity
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The equation XZAYZ+1A+e-10+v¯   represents- 
1. β-emission             

2. α-emission

3. e- capture             

4. Fission

Concept Questions :-

Types of decay
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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 
(a) A1t1=A2t2            (b) A1-A2=t2-t1
(c) A2=A1et1-t2/T    (d) A2=A1et1/t2T

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

(a) YZ+2A+4                     (b) YZA
(c) YZ-2A-4                     (d) YZ-4A-2

Concept Questions :-

Types of decay
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