Chapter 21

What should be the age of fossil for meaningful determination of its age? (a) 6 years (b) 6000 years (c) 60,000 years (d) It can be used to calculate any age [IIT 2006]

Nuclear explosion has taken place leading to increase in concentration of \({ }^{14} \mathrm{C}\) in nearby areas. \({ }^{14} \mathrm{C}\) concentration is \(\mathrm{C}_{1}\) in nearby areas and \(\mathrm{C}_{2}\) in areas far away. If the age of the fossil is determined to be \(\mathrm{T}_{1}\) and \(\mathrm{T}_{2}\) at the places respectively then (a) The age of the fossil will increase at the place where explosion has taken place and \(\mathrm{T}_{1}-\mathrm{T}_{2}=\frac{1}{\lambda} \ln \frac{\mathrm{C}_{1}}{\mathrm{C}_{2}}\) (b) The age of the fossil will decrease at the place where explosion has taken place and \(\mathrm{T}_{1}-\mathrm{T}_{2}=\frac{1}{\lambda} \operatorname{In} \frac{\mathrm{C}_{1}}{\mathrm{C}_{2}}\) (c) The age of fossil will be determined to be same (d) \(\mathrm{T}_{1} / \mathrm{T}_{2}=\mathrm{C}_{1} / \mathrm{C}_{2}\) [IIT 2006]

$$ \text { Match the following } $$$$ \begin{array}{ll} \hline \text { Column-I (Reactions) } & \begin{array}{l} \text { Column-II } \\ \text { (Particles) } \end{array} \\ \hline \text { (a) }{\underline{\phantom{xx}}}_{4} \mathrm{Be}^{9}+{ }_{2} \mathrm{He}^{4} \rightarrow{ }_{6} \mathrm{C}^{12}+\ldots \ldots & \text { (p) }{\underline{\phantom{xx}}}_{2} \mathrm{He}^{4} \\ \text { (b) }{\underline{\phantom{xx}}}_{6} \mathrm{C}^{12}+\ldots \ldots \rightarrow{ }_{5} \mathrm{~B}^{10}+{ }_{2} \mathrm{He}^{4} & \text { (q) }{\underline{\phantom{xx}}}_{0} \mathrm{n}^{1} \\\ \text { (c) }{\underline{\phantom{xx}}}_{7} \mathrm{~N}^{14}+\ldots \ldots \rightarrow{ }_{8} \mathrm{O}^{17}+{ }_{1} \mathrm{H}^{1} & \text { (r) }, \mathrm{D}^{2} \\ \text { (d) }{\underline{\phantom{xx}}}_{20} \mathrm{Ca}^{40}+\ldots . . \rightarrow{ }_{19} \mathrm{~K}^{37}+{ }_{2} \mathrm{He}^{4} & \text { (s) }{\underline{\phantom{xx}}}_{1} \mathrm{H}^{1} \\\ \hline \end{array} $$

The disintegration rate of a certain radioactive sample at any instant is 5400 dpm. After 5 min the rate becomes 2700 dpm. The half life of the sample in min is approximately

Half-life of a substance A, following first order kinetics is 5 days. Starting with \(100 \mathrm{~g}\) of \(\mathrm{A}\), amount left after 15 days is \(|\mathbf{2 0 0 2}|\) (a) \(25 \mathrm{~g}\) (b) \(50 \mathrm{~g}\) (c) \(12.5 \mathrm{~g}\) (d) \(6.25 \mathrm{~g}\)

\(\beta\) particle is emitted in a radioactive reaction when [2002] (a) a proton changes to neutron (b) a neutron changes to proton (c) a neutron changes to electron (d) an electron changes to neutron

The radio nucliede \({ }_{90} \mathrm{Th}^{234}\) undergoes two successive \(\beta\) decays followed by one \(\alpha\) decay. The atomic number and the mass number respectively of the resulting radio nucliede will be (a) 92 and 234 (b) 94 and 230 (c) 90 and 230 (d) 92 and 230

The half-life of a radioactive isotope is three hours. If the initial mass of the isotope were \(256 \mathrm{~g}\), the mass of it remaining undecayed after 18 hours would be \([2003]\) (a) \(4.0 \mathrm{~g}\) (b) \(8.0 \mathrm{~g}\) (c) \(12 . \overline{0} \mathrm{~g}\) (d) \(16.0 \mathrm{~g}\)

The half-life of a radio isotope is four hours. If the initial mass of the isotope was \(200 \mathrm{~g}\) the mass remaining undecayed after 24 hours is (a) \(2.084 \mathrm{~g}\) (b) \(3.125 \mathrm{~g}\) (c) \(4.167 \mathrm{~g}\) (d) \(1.042 \mathrm{~g}\)

A photon of hard \(\gamma\) radiation knocks a proton out of \({ }_{12} \mathrm{Mg}^{44}\) nucleus to form [2005] (a) the isotope of parent nucleus (b) the isobar of parent nucleus (c) the nuclide of \({ }_{11} \mathrm{Na}^{23}\) (d) the isobar of \({ }_{11} \mathrm{Na}^{23}\)

Hydrogen bomb is based on the principle of \(\quad\) [2005] (a) artificial radioactivity (b) nuclear fission (c) nuclear fusion (d) natural radioactivity

In the transformation of \({ }_{92} \mathrm{U}^{238}\) to \({ }_{92} \mathrm{U}^{234}\), if one emission is an \(\alpha\) particle, what should be the other emission(s)? \([2006]\) (a) two \(\beta\) (b) two \(\beta\) and one \(\beta^{+}\) (c) one \(\beta\) - and one \(\gamma\) (d) one \(\beta\) and one \(\beta\)

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how manydays will it be safe to enter the room? \(\quad\) [2007] (a) 300 days (b) 10 days (c) 100 days (d) 1000 days

Which of the following nuclear reactions will generate an isotope? \([2007]\) (a) positron emission (b) \(\alpha\) particle emission (c) \(\beta\) particle emission (d) neutron particle emission