The half life of the isotope Na1124 is 15 hrs. How much time does it take for 78th of a sample of this isotope to decay

(a) 75 hrs               (b) 65 hrs
(c) 55 hrs               (d) 45 hrs

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Radioactivity
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If the half life of a radioactive sample is 10 hours,
its mean life is 
(a) 14.4 hours               (b) 7.2 hours
(c) 20 hours                  (d) 6.93 hours

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Radioactivity
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If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in 4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm 
(a) In 8 minutes              (b) In 12 minutes
(c) In 16 minutes             (d) In 20 minutes

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16 gm sample of a radioactive element is taken from Bombay to Delhi in 2 hour and it was found that 1 gm of the element remained (undisintegrated). Half life of the element is 
(a) 2 hour           (b) 1 hour
(c) 12 hour         (d) 14hour

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Radioactivity
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Unit of radioactivity is Rutherford. Its value is

(a) 3.7×1010 disintegrations/sec
(b) 3.7×106 disintegrations/sec
(c) 1.0×1010disintegrations/sec
(d) 1.0×106 disintegrations/sec

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Radioactivity
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A radioactive substance has a half life of 60 minutes. After 3 hours, the fraction of atom that have decayed would be

(a) 12.5%               (b) 87.5%
(c) 8.5%                 (d) 25.1%

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Radioactivity
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An element used for radioactive carbon dating for more than 5600 years is 
(a) C-14          (b) U-234
(c) U-238        (d) Po-94

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Radioactivity
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N atoms of a radioactive element emit n alpha particles per second. The half life of the element is

(a) nN sec                    (b) Nn sec
(c) 0.693 Nn sec           (d)  0.693 nN sec

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Radioactivity
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The radioactive nucleus N713 decays to C613 through the emission of 
(a) Neutron              (b) Proton
(c) Electron              (d) Positron

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The radioactive decay of uranium into thorium is expressed by the equation U92238Th90234+X where 'X' is

(a) An electron                (b) A proton
(c) A deuteron                 (d) An alpha particle

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Radioactivity
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