Chapter 21

Which of the following statements is/are incorrect, when the nuclide, \({ }_{19} \mathrm{~K}^{40}\), is subject to \(\mathrm{K}\)-electron capture? (a) \({ }^{40} \mathrm{Ar}\) is produced with emission of \(\beta\)-particle. (b) \({ }^{40} \mathrm{Ar}\) is produced with emission of \(\alpha\)-particles. (c) \({ }^{40} \mathrm{Ar}\) is produced without emission of radiation (d) \({ }^{40} \mathrm{Ar}\) is produced with emission of X-radiation.

An unstable nucleus is characterized by (i) \(\mathrm{n} / \mathrm{p}>1\) (ii) low binding energy (iii) high temperature and pressure (iv) high packing fraction (a) (i), (ii) (b) (i), (ii), (iv) (c) (i), (ii), (iii) (d) (i), (ii), (iii), (iv)

How much time is required for a \(5.75\)-mg sample of \({ }^{51} \mathrm{Cr}\) to decay to \(1.50 \mathrm{mg}\) if it has a half-life of \(27.8\) days? (a) \(5.39\) days (b) \(2.69\) days (c) \(53.9\) days (d) \(5.49\) days

Potassium \(-40\) decays to argon \(-40\) with a half life of \(1.27 \times 10^{9} \mathrm{yr}\). What is the age of a rock in which the mass ratio of \({ }^{40} \mathrm{Ar}\) to \({ }^{40} \mathrm{~K}\) is \(3.6\) ? (a) \(2.8 \times 10^{10} \mathrm{yr}\) (b) \(1.4 \times 10^{9} \mathrm{yr}\) (c) \(1.4 \times 10^{10} \mathrm{yr}\) (d) \(2.8 \times 10^{9} \mathrm{yr}\)

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

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

Match the following Column-I (a) \(\mathrm{P}^{32}\) (b) \(\mathrm{Na}^{24}\) (c) \(\mathrm{Co}^{60}\) (d) \(I^{131}\) Column-II (p) Location of tumour in the brain (q) Location of blood clots and circulatory disorders (r) Radiotherapy (s) Agricultural research

Match the lists I and II and pick the correct matching from the codes given below, Column-I (a) Isotope (b) Isobar (c) Isotone (d) Isosters (e) Isodiaphers Column-II (p) \({ }_{88} \mathrm{Ra}^{228}\) and \({ }_{89} \mathrm{Ac}^{228}\) (q) \({ }_{18} \mathrm{Ar}^{39}\) and \({ }_{19} \mathrm{~K}^{40}\) (r) \({ }_{1} \mathrm{H}^{2}\) and \({ }_{1} \mathrm{H}^{3}\) (s) \({ }_{92} \mathrm{U}^{235}\) and \(_{90}^{\mathrm{Th} 231}\) (t) \(\mathrm{CO}_{2}\) and \(\mathrm{N}_{2} \mathrm{O}\)

A fresh radioactive mixture containing short lived species \(X\) and \(Y\). Both the species together emitting \(8000 \alpha\) - particles per minute initially. 20 minutes later \(X\) was emitting \(\alpha-\) particles at the rate of 4500 per minute. If the half lives of the species \(\mathrm{X}\) and \(\mathrm{Y}\) are 10 minute and 500 hours, then what is the ratio of initial activities of \(X\) and \(Y\) in the mixture?

The disintegration rate of a certain radioactive sample at any instant is \(5400 \mathrm{dpm}\). After 5 min the rate becomes \(2700 \mathrm{dpm}\). 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 (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 \({ }_{90}\) 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) \(12.0 \mathrm{~g}\) (d) \(16.0 \mathrm{~g}\)

Consider the following nuclear reactions \({ }_{92} \mathrm{M}^{238} \longrightarrow \mathrm{y}^{\mathrm{N}}^{\mathrm{x}}+2{ }_{2} \mathrm{He}^{4}\) \({ }_{\mathrm{y}} \mathrm{N}^{\mathrm{x}} \longrightarrow{\mathrm{B}} \mathrm{L}^{\mathrm{A}}+2 \beta^{+}\) The number of neutrons in element \(\mathrm{L}\) is (a) 146 (b) 144 (c) 142 (d) 140

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 (a) the isotope of parent nucleus (b) the isobar of parent nucleus (c) the nuclide of \({ }_{14} \mathrm{Na}^{23}\) (d) the isobar of \(_{11} \mathrm{Na}^{23}\)

Hydrogen bomb is based on the principle of (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 many days will it be safe to enter the room? (a) 300 days (b) 10 days (c) 100 days (d) 1000 days

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