The radioactive decay of uranium into thorium is expressed by the equation ${}_{92}{}^{238}\mathrm{U}\to {}_{90}{}^{234}\mathrm{Th}+\mathrm{X}$ where 'X' is

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

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In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following would be emitted in the decay process
(a) Proton              (b) Neutron
(c) Electron            (d) Photon

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The half life (T) and the disintegration constant $\mathrm{\lambda }$ of a radioactive substance are related as
(a) $\mathrm{\lambda T}=1$                     (b) $\mathrm{\lambda T}=0.693$
(c) $\frac{\mathrm{T}}{\mathrm{\lambda }}=0.693$              (d) $\frac{\mathrm{\lambda }}{\mathrm{T}}=0.693$

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The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be

(a) 93.75%                  (b) 75%
(c) 25%                       (d) 6.25%

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In the uranium radioactive series, the initial nucleus is ${}_{92}{}^{238}\mathrm{U}$ and the final nucleus is ${}_{82}{}^{206}\mathrm{Pb}$. When the uranium nucleus decays to lead, the number of  $\mathrm{\alpha }$-particles emitted will be
(a) 1                (b) 2
(c) 4                (d) 8

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Types of decay
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Which of the following is a correct statement

(a) Beta rays are same as cathode rays
(b) Gamma rays are high energy neutrons
(c) Alpha particles are singly ionized helium atoms
(d) Protons and neutrons have exactly the same mass

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Types of decay
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${}_{22}\mathrm{Ne}$ nucleus after absorbing energy decays into two $\mathrm{\alpha }$-particles and an unknown nucleus. The unknown nucleus is
(a) Nitrogen              (b) Carbon
(c) Boron                  (d) Oxygen

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Types of decay
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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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