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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If half-life of a radioactive atom is 2.3 days, then its decay constant would be
(a) 0.1            (b) 0.2
(c) 0.3            (d) 2.3

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A radioactive element ${}_{90}{}^{238}\mathrm{X}$ decay into ${}_{83}{}^{222}\mathrm{Y}$. The number of $\mathrm{\beta }$-particles emitted are

(a) 4             (b) 6
(c) 2             (d) 1

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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

(a) 66.6%               (b) 85.5%
(c) 62.5%               (d) 75%

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An artificial radioactive decay series begins with unstable ${}_{94}{}^{241}\mathrm{Pu}$. The stable nuclide obtained after eight α decays and five $\mathrm{\beta }$-decays is
(a) ${}_{83}{}^{209}\mathrm{Bi}$          (b) ${}_{82}{}^{209}\mathrm{Pb}$
(c) ${}_{82}{}^{205}\mathrm{Ti}$          (d) ${}_{82}{}^{201}\mathrm{Hg}$

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