Title 24. Atomic Physics -3 Easy.pdf ✅

1. A radioactive reaction is 206 82 238 92U → Pb . How many  and  particles are emitted (a) 10, 6 (b) 4 protons, 8 neutrons (c) 6 electrons, 8 protons (d) 6, 8 2. A radioactive substance has a half life of 60 minutes. After 3 hours, the fraction of atom that have decayed would be (a) 12.5% (b) 87.5% (c) 8.5% (d) 25.1% 3. A element used for radioactive carbon dating for more than 5600 years is (a) C −14 (b) U − 234 (c) U − 238 (d) Po −94 4. After two hours, one- sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is (a) 15 minutes (b) 30 minutes (c) 45 minutes (d) 1 hour 5. N atoms of a radioactive element emit n alpha particles per second. The half life of the element is (a) N n sec (b) n N sec (c) n 0.693 N sec (d) N 0.693 n sec 6. A radioactive nucleus 235 92 X decays to 231 91Y . Which of the following particles are emitted (a) One alpha and one electron (b) Two deuterons and one positron (c) One alpha and one proton (d) One proton and four neutrons 7. The radioactive nucleus 13 7 N decays to 13 6C through the emission of (a) Neutron (b) Proton (c) Electron (d) Positron 8. The counting rate observed from a radioactive source at t=0 second was 1600 counts per second and at t=8 seconds it was 100 counts per second. The counting rate observed, as counts per second at t=6 seconds, will be (a) 400 (b) 300 (c) 200 (d) 150 9. The radioactive decay of uranium into thorium is expressed by the equation , 234 90 238 92 U → Th + X where ' X' is (a) An electron (b) A proton (c) A deuteron (d) An alpha particle 10. The relationship between  and half life ( ) T1 / 2 of a radioactive substance is (a) 1 / 2 10 log 2 T  = (b) 1 / 2 log 2 T e  = (c) 1 / 2 2 log 10 T  = (d) 1 / 2 2 log T e  = 11. 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 12. The rate of disintegration of fixed quantity of a radioactive element can be increased by (a) Increasing the temperature (b) Increasing the pressure (c) Chemical reaction (d) It is not possible 13. The half life (T) and the disintegration constant () of a radioactive substance are related as (a) T = 1 (b) T = 0.693 (c) = 0.693  T (d) = 0.693 T  14. 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% 15. Radon (Ra) decays into Polonium ( P0 ) by emitting an  − particle with half-life of 4 days. A sample contains 10 6.4 10 atoms of Rn . After 12 days, the number of atoms of Rn left in the sample will be (a) 10 3.2 10 (b) 10 0.53 10 (c) 10 2.1 10 (d) 10 0.8 10 16. Decay constant of radium is  . By a suitable process its compound radium bromide is obtained. The decay constant of radium bromide will be (a)  (b) More than  (c) Less than  (d) Zero 17. In the uranium radioactive series, the initial nucleus is 238 92U and the final nucleus is 206 82Pb . When the uranium nucleus decays to lead, the number of  − particles emitted will be (a) 1 (b) 2
(c) 4 (d) 8 18. After 1 and 2 emissions (a) Mass number reduces by 3 (b) Mass number reduces by 4 (c) Mass number reduces by 6 (d) Atomic number remains unchanged 19. 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 20. Ne 22 nucleus after absorbing energy decays into two  − particles and an unknown nucleus. The unknown nucleus is (a) Nitrogen (b) Carbon (c) Boron (d) Oxygen 21. Half lives of two radioactive substances A and B are respectively 20 minutes and 40 minutes. Initially the sample of A and B have equal number of nuclei. After 80 minutes, the ratio of remaining number of A and B nuclei is (a) 1 : 16 (b) 4 : 1 (c) 1 : 4 (d) 1 : 1 22. A nucleus m n X emits one  and one  particles. The resulting nucleus is (a) m −4 n X (b) 4 2 − − m n Y (c) 4 4 − − m n Z (d) 4 1 − − m n Z 23. If the radioactive decay constant of radium is 4 1.07 10 −  per year, then its half life period is approximately equal to (a) 8,900 years (b) 7,000 years (c) 6,476 years (d) 2,520 years 24. The half life of I 131 is 8 days. Given a sample of I 131 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 25. 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 4 1 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 26. Age of a tree is determined using radio-isotope of (a) Carbon (b) Cobalt (c) Iodine (d) Phosphorus 27. An atom of mass number 15 and atomic number 7 captures an  − particle and then emits a proton. The mass number and atomic number of the resulting product will respectively be (a) 14 and 2 (b) 15 and 3 (c) 16 and 4 (d) 18 and 8 28. Which of the following statements are true regarding radioactivity (I) All radioactive elements decay exponentially with time (II) Half life time of a radioactive element is time required for one half of the radioactive atoms to disintegrate (III) Age of earth can be determined with the help of radioactive dating (IV) Half life time of a radioactive element is 50% of its average life period Select correct answer using the codes given below Codes : (a) I and II (b) I, III and IV (c) I, II and III (d) II and III 29. In the disintegration series U X Y A ⎯⎯→ ⎯ ⎯→Z 238   − 92 the values of Z and A respectively will be (a) 92, 236 (b) 88, 230 (c) 90, 234 (d) 91, 234 30. The particles emitted by radioactive decay are deflected by magnetic field. The particles will be (a) Protons and  − particles (b) Electrons, protons and  − particles (c) Electrons, protons and neutrons (d) Electrons and  − particles 31. 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 32. In the given nuclear reaction A, B, C, D, E represents 234 9 2 238 9 2U Th Pa U C E D A ⎯⎯ →B ⎯⎯ → ⎯⎯→ (a) A = 234, B = 90, C = 234, D = 91, E =  (b) A = 234, B = 90, C = 238, D = 94, E =  (c) A = 238, B = 93, C = 234, D = 91, E =  (d) A = 234, B = 90, C = 234, D = 93, E = 
33. 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 34. The nucleus Cd 115 48 after two successive −  decays will give (a) Pa 115 46 (b) In 114 49 (c) Sn 113 50 (d) Sn 115 50 35. A radioactive sample with a half life of 1 month has the label : “Activity=2 micro curies on 1.8.1991.'' What will be its activity two months later (a) 1.0 micro curies (b) 0.5 micro curies (c) 4 micro curies (d) 8 micro curies 36. An element A decays into element C by a two step process : 4 A → B + 2He− B → C + 2e Then (a) A and C are isotopes (b) A and C are isobars (c) A and B are isotopes (d) A and B are isobars 37. 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 38. Which of the following isotopes is used for the treatment of cancer (a) 40 K (b) 60 Co (c) 90 Sr (d) 131 I 39. 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 40. A radioactive element 238 90 X decay into 222 83Y . The number of  − particles emitted are (a) 4 (b) 6 (c) 2 (d) 1 41. 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% 42. The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 and as 975 counts per minute at t = 5 minutes. The decay constant is approximately (a) 0.230 per minute (b) 0.461 per minute (c) 0.691 per minute (d) 0.922 per minute 43. An artificial radioactive decay series begins with unstable Pu 241 94 . The stable nuclide obtained after eight  − decays and five  − decays is (a) Bi 209 83 (b) Pb 209 82 (c) Ti 205 82 (d) Hg 201 82 44. The activity of a sample is 64 × 10–5 Ci. Its half-life is 3 days. The activity will become 5 × 10–6 Ci after (a) 12 days (b) 7 days (c) 18 days (d) 21 days 45. Consider the following two statements A. Energy spectrum of -particles emitted in radioactive decay is discrete B. Energy spectrum of -particles emitted in radioactive decay is continuous (a) Only A is correct (b) Only B is correct (c) A is correct but B is wrong (d) Both A and B are correct 46. The half-life of radon is 3.8 days. Three forth of a radon sample decay in (a) 5.02 days (b) 15.2 days (c) 7.6 days (d) 11.4 days 47. A nucleus of an element 202 84 X emits an -particle first, a - particle next and then a gamma photon. The final nucleus formed has an atomic number (a) 200 (b) 199 (c) 83 (d) 198 48. 3.8 days is the half-life period of a sample. After how many days, the sample will become 1/8th of the original substance (a) 11.4 (b) 3.8 (c) 3 (d) None of these 49. Plutonium decays with a half-life of 24000 years. If the plutonium is stored for 72000 years, then the fraction of plutonium that remains is (a) 2 1 (b) 3 1 (c) 4 1 (d) 8 1
50. A radioactive substance emits (a) -rays (b) -rays (c) -rays (d) All of these 51. The large scale destruction, that would be caused due to the use of nuclear weapons is called (a) Nuclear holocaust (b) Thermo-nuclear reaction (c) Nuetron reproduction factor (d) None of these 52. An atomic nucleus 232 90Th emits several  and  radiations and finally reduces to 208 82Pb . It must have emitted (a) 4 and 2 (b) 6 and 4 (c) 8 and 24 (d) 4 and 16 53. In beta decay (a) The parent and daughter nuclei have same number of protons (b) The daughter nucleus has one proton less than the parent nucleus (c) The daughter nucleus has one proton more than the parent nucleus (d) The daughter nucleus has one neutron more than the parent nucleus 54. A radioactive substance has a half-life of 1 year. The fraction of this material, that would remain after 5 years will be (a) 32 1 (b) 5 1 (c) 2 1 (d) 5 4 55. The activity of a radioactive sample (a) Can be increased by heating it (b) Is independent of physical parameter (c) Cannot be increased by any method (d) Both (b) and (c) 56. A radioactive sample has half-life of 5 years. Probability of decay in 10 years will be (a) 100% (b) 75% (c) 50% (d) 25% 57. If half-life of a substance is 3.8 days and its quantity is 10.38 gm. Then substance quantity remaining left after 19 days will be (a) 0.151 gm (b) 0.32 gm (c) 1.51 gm (d) 0.16 gm 58. After five half lives what will be the fraction of initial substance (a) 10 2 1       (b) 5 2 1       (c) 4 2 1       (d) 3 2 1       59. Which is the correct expression for half-life (a) ( ) log 2 t 1/ 2 = (b) log 2 ( ) 1 / 2  t = (c) (2.303 ) log 2 ( )1 / 2  t = (d)  2.303 log 2 ( )t 1/ 2 = 60. A nucleus X A Z emits an -particle. The resultant nucleus emits a +  particle. The respective atomic and mass no. of the final nucleus will be (a) Z – 3, A – 4 (b) Z – 1, A – 4 (c) Z – 2, A – 4 (d) Z, A – 2 61. What fraction of a radioactive material will get disintegrated in a period of two half-lives (a) Whole (b) Half (c) One-fourth (d) Three-fourth 62. The activity of a radioactive sample is 1.6 curie and its half-life is 2.5 days. Its activity after 10 days will be (a) 0.8 curie (b) 0.4 curie (c) 0.1 curie (d) 0.16 curie 63. In a mean life of a radioactive sample (a) About 1/3 of substance disintegrates (b) About 2/3 of the substance disintegrates (c) About 90% of the substance disintegrates (d) Almost all the substance disintegrates 64. Three fourth of the active decays in a radioactive sample in 3/4 sec. The half life of the sample is (a) 2 1 sec (b) 1 sec (c) 8 3 sec (d) 4 3 sec 65. During mean life of a radioactive element, the fraction that disintegrates is (a) e (b) e 1 (c) e e −1 (d) e − 1 e 66. 1 Curie is equal to (a) 10 3  10 disintegrations/sec (b) 7 3.7 10 disintegrations/sec