The half life of ${}_{131}\mathrm{I}$ is 8 days. Given a sample of ${}_{131}\mathrm{I}$ at time t = 0, we can assert that
(a) No nucleus will decay before t = 4 days
(b) No nucleus will decay before t = 8 days
(c) All nuclei will decay before t = 16 days
(d) A given nucleus may decay at any time after t = 0

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Carbon-14 decays with half-life of about 5,800 years. In a sample of bone, the ratio of carbon-14 to carbon-12 is found to be $\frac{1}{4}$ of what it is in free air. This bone may belong to a period about x centuries ago, where x is nearest to
(a) 2$×$58                        (b) 58
(c) 58/2                          (d) 3$×$58

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In the disintegration series ${}_{92}{}^{238}\mathrm{U}\stackrel{\mathrm{\alpha }}{\to }\mathrm{X}\stackrel{\mathrm{\beta }-}{\to }{}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{Y}$
the values of Z and A respectively will be
(a) 92, 236                (b) 88, 230
(c) 90, 234                (d) 91, 234

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The particles emitted by radioactive decay are deflected by magnetic field. The particles will be
(a) Protons and $\mathrm{\alpha }$-particles
(b) Electrons, protons and $\mathrm{\alpha }$-particles
(c) Electrons, protons and neutrons
(d) Electrons and $\mathrm{\alpha }$-particles

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Types of decay

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Half life of a radioactive element is 10 days. The time during which quantity remains 1/10 of initial mass will be
(a) 100 days             (b) 50 days
(c) 33 days               (d) 16 days

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In the given nuclear reaction A, B, C, D, E represents
${}_{92}{}^{238}\mathrm{U}\stackrel{\mathrm{\alpha }}{\to }{}_{\mathrm{B}}{}^{\mathrm{A}}\mathrm{Th}\stackrel{\mathrm{\beta }}{\to }{}_{\mathrm{D}}{}^{\mathrm{C}}\mathrm{Pa}\stackrel{\mathrm{E}}{\to }{}_{92}{}^{234}\mathrm{U}$

(a) A = 234, B = 90, C = 234, D = 91, E = $\mathrm{\beta }$
(b) A = 234, B = 90, C = 238, D = 94, E =$\mathrm{\alpha }$
(c) A = 238, B = 93, C = 234, D = 91, E = $\mathrm{\beta }$
(d) A = 234, B = 90, C = 234, D = 93, E = $\mathrm{\alpha }$

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Types of decay
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If half life of a radioactive element is 3 hours, after 9 hours its activity becomes
(a) 1/9                     (b) 1/27
(c) 1/6                     (d) 1/8

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The nucleus ${}_{48}{}^{115}\mathrm{Cd}$ after two successive ${\mathrm{\beta }}^{-}$ decays will give
(a) ${}_{46}{}^{115}\mathrm{Pa}$          (b) ${}_{49}{}^{114}\mathrm{In}$
(c) ${}_{50}{}^{113}\mathrm{Sn}$          (d) ${}_{50}{}^{115}\mathrm{Sn}$

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Types of decay
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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
(a) 1 : 1                 (b) 2 : 1
(c) 1 : 2                 (d) 1 : 4

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Which of the following isotopes is used for the treatment of cancer
(a) ${\mathrm{K}}^{40}$         (b) ${\mathrm{Co}}^{60}$
(c) ${\mathrm{Sr}}^{90}$        (d) ${\mathrm{I}}^{131}$

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