JEE Physics Nuclei MCQs Set 21

Practice MCQs for JEE Physics Nuclei

Access targeted multiple-choice questions for Nuclei designed to align with the latest JEE academic syllabus for JEE Physics. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Access Nuclei Questions and Solutions

Access the complete set of multiple-choice questions for Nuclei below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official JEE textbooks.

Multiple Choice Questions

Question 1: Choose the true statement.
(a) The energy released per unit mass is more in fusion than in fission, and that per atom is more in fission
(b) The energy released per unit mass is more in fission than in fusion
(c) The energy released per atom is more in fusion than in fission
(d) Both release the same energy per atom as well as per unit mass
Show Answer & Explanation

Answer: (a) The energy released per unit mass is more in fusion than in fission, and that per atom is more in fission

Explanation:
1. Fission of one uranium atom gives about 200 MeV, fusion of two deuterons about 24 MeV, so per atom fission gives more.
2. Per unit mass fusion gives more (for example about 3.5 MeV per nucleon in D-T fusion against about 0.85 MeV per nucleon in fission).

Teacher's Note:
1. H
2. e
3. a
4. v
5. y
6.
7. n
8. u
9. c
10. l
11. e
12. i
13.
14. h
15. a
16. v
17. e
18.
19. m
20. a
21. n
22. y
23.
24. n
25. u
26. c
27. l
28. e
29. o
30. n
31. s
32.
33. p
34. e
35. r
36.
37. e
38. v
39. e
40. n
41. t
42. ,
43.
44. l
45. i
46. g
47. h
48. t
49.
50. n
51. u
52. c
53. l
54. e
55. i
56.
57. h
58. a
59. v
60. e
61.
62. f
63. e
64. w
65. ,
66.
67. w
68. h
69. i
70. c
71. h
72.
73. r
74. e
75. v
76. e
77. r
78. s
79. e
80. s
81.
82. t
83. h
84. e
85.
86. c
87. o
88. m
89. p
90. a
91. r
92. i
93. s
94. o
95. n
96.
97. b
98. e
99. t
100. w
101. e
102. e
103. n
104.
105. p
106. e
107. r
108. -
109. a
110. t
111. o
112. m
113.
114. a
115. n
116. d
117.
118. p
119. e
120. r
121. -
122. m
123. a
124. s
125. s
126.
127. e
128. n
129. e
130. r
131. g
132. y
133. .

Question 2: In a uranium reactor of thermal power 100 MW, the average number of neutrons liberated in each fission is 2.5 and each fission releases 200 MeV. The number of neutrons generated per second is:
(a) \( 4\times10^{18}\ \mathrm{s^{-1}} \)
(b) \( \frac{125}{16}\times10^{18}\ \mathrm{s^{-1}} \)
(c) \( 8\times10^{23}\ \mathrm{s^{-1}} \)
(d) \( 8\times10^{19}\ \mathrm{s^{-1}} \)
Show Answer & Explanation

Answer: (b) \( \frac{125}{16}\times10^{18}\ \mathrm{s^{-1}} \)

Explanation:
1. Fissions per second \( =\frac{10^8}{200\times1.6\times10^{-13}}=3.125\times10^{18} \).
2. Neutrons per second \( =2.5\times3.125\times10^{18}=7.8\times10^{18}=\frac{125}{16}\times10^{18} \).

Teacher's Note:
1. D
2. i
3. v
4. i
5. d
6. e
7.
8. t
9. h
10. e
11.
12. p
13. o
14. w
15. e
16. r
17.
18. b
19. y
20.
21. t
22. h
23. e
24.
25. e
26. n
27. e
28. r
29. g
30. y
31.
32. p
33. e
34. r
35.
36. f
37. i
38. s
39. s
40. i
41. o
42. n
43.
44. t
45. o
46.
47. g
48. e
49. t
50.
51. t
52. h
53. e
54.
55. f
56. i
57. s
58. s
59. i
60. o
61. n
62.
63. r
64. a
65. t
66. e
67. ,
68.
69. t
70. h
71. e
72. n
73.
74. m
75. u
76. l
77. t
78. i
79. p
80. l
81. y
82.
83. b
84. y
85.
86. t
87. h
88. e
89.
90. n
91. e
92. u
93. t
94. r
95. o
96. n
97. s
98.
99. p
100. e
101. r
102.
103. f
104. i
105. s
106. s
107. i
108. o
109. n
110. .

Question 3: Free U-238 nuclei kept in a train emit alpha particles. When the train is stationary and a nucleus decays, a passenger measures the separation between the alpha particle and the recoiling nucleus as x at time t. If the decay occurs when the train moves at uniform speed v, the distance measured by the passenger at time t after the decay is:
(a) x + vt
(b) x - vt
(c) x
(d) It depends on the direction of the train
Show Answer & Explanation

Answer: (c) x

Explanation:
1. A train moving at uniform speed is an inertial frame, and the physics of the decay is the same in every inertial frame.
2. The relative velocity of the two fragments, as measured by the passenger, is unchanged, so the separation at time t is again x.

Teacher's Note:
1. R
2. e
3. l
4. a
5. t
6. i
7. v
8. e
9.
10. m
11. o
12. t
13. i
14. o
15. n
16.
17. b
18. e
19. t
20. w
21. e
22. e
23. n
24.
25. t
26. w
27. o
28.
29. o
30. b
31. j
32. e
33. c
34. t
35. s
36.
37. d
38. o
39. e
40. s
41.
42. n
43. o
44. t
45.
46. d
47. e
48. p
49. e
50. n
51. d
52.
53. o
54. n
55.
56. t
57. h
58. e
59.
60. u
61. n
62. i
63. f
64. o
65. r
66. m
67.
68. v
69. e
70. l
71. o
72. c
73. i
74. t
75. y
76.
77. o
78. f
79.
80. t
81. h
82. e
83.
84. o
85. b
86. s
87. e
88. r
89. v
90. e
91. r
92. .

Question 4: For a nucleus of mass number A and radius R, the graph of \( \ln(R/R_0) \) versus \( \ln A \) is:
(a) a parabola
(b) an ellipse
(c) a hyperbola
(d) a straight line
Show Answer & Explanation

Answer: (d) a straight line

Explanation:
1. From \( R=R_0A^{1/3} \) we get \( \ln\frac{R}{R_0}=\tfrac13\ln A \).
2. This has the form y = mx with slope 1/3, a straight line through the origin.

Teacher's Note:
1. T
2. a
3. k
4. i
5. n
6. g
7.
8. l
9. o
10. g
11. a
12. r
13. i
14. t
15. h
16. m
17. s
18.
19. t
20. u
21. r
22. n
23. s
24.
25. a
26.
27. p
28. o
29. w
30. e
31. r
32.
33. l
34. a
35. w
36.
37. i
38. n
39. t
40. o
41.
42. a
43.
44. l
45. i
46. n
47. e
48. a
49. r
50.
51. r
52. e
53. l
54. a
55. t
56. i
57. o
58. n
59. .
60.
61. T
62. h
63. e
64.
65. s
66. l
67. o
68. p
69. e
70.
71. o
72. f
73.
74. t
75. h
76. e
77.
78. l
79. i
80. n
81. e
82.
83. i
84. s
85.
86. t
87. h
88. e
89.
90. e
91. x
92. p
93. o
94. n
95. e
96. n
97. t
98. ,
99.
100. 1
101. /
102. 3
103. .

Question 5: The binding energy per nucleon of lithium-7 (\( {}^7_3Li \)) is nearly (masses: \( {}^7_3Li=7.014353 \) u, \( {}^1_1H=1.007826 \) u, neutron \( 1.00867 \) u; 1 u = 931 MeV):
(a) 5.83 MeV
(b) 40.8 MeV
(c) 4.08 MeV
(d) 7.0 MeV
Show Answer & Explanation

Answer: (a) 5.83 MeV

Explanation:
1. Mass defect \( \Delta m=3(1.007826)+4(1.00867)-7.014353=0.043805 \) u.
2. Binding energy \( =0.043805\times931=40.8 \) MeV.
3. Per nucleon \( 40.8/7=5.83 \) MeV.

Teacher's Note:
1. U
2. s
3. i
4. n
5. g
6.
7. a
8. t
9. o
10. m
11. i
12. c
13.
14. m
15. a
16. s
17. s
18. e
19. s
20.
21. f
22. o
23. r
24.
25. h
26. y
27. d
28. r
29. o
30. g
31. e
32. n
33.
34. a
35. u
36. t
37. o
38. m
39. a
40. t
41. i
42. c
43. a
44. l
45. l
46. y
47.
48. a
49. c
50. c
51. o
52. u
53. n
54. t
55. s
56.
57. f
58. o
59. r
60.
61. t
62. h
63. e
64.
65. e
66. l
67. e
68. c
69. t
70. r
71. o
72. n
73. s
74.
75. o
76. f
77.
78. t
79. h
80. e
81.
82. l
83. i
84. t
85. h
86. i
87. u
88. m
89.
90. a
91. t
92. o
93. m
94. .

Question 6: Which of the following processes represents a gamma decay?
(a) \( {}^A_ZX+\gamma\to{}^A_{Z-1}X+a+b \)
(b) \( {}^A_Z X\to{}^A_ZX+f \) (a photon f is emitted)
(c) \( {}^A_ZX+{}^1_0n\to{}^{A-3}_{Z-2}X+c \)
(d) \( {}^A_ZX+e^-\to{}^A_{Z-1}X+g \)
Show Answer & Explanation

Answer: (b) \( {}^A_Z X\to{}^A_ZX+f \) (a photon f is emitted)

Explanation:
1. In gamma decay the nucleus drops from an excited level to a lower level: A and Z are unchanged and only a photon is emitted.
2. The other options change Z or A.

Teacher's Note:
1. O
2. n
3. l
4. y
5.
6. t
7. h
8. e
9.
10. o
11. p
12. t
13. i
14. o
15. n
16.
17. i
18. n
19.
20. w
21. h
22. i
23. c
24. h
25.
26. b
27. o
28. t
29. h
30.
31. A
32.
33. a
34. n
35. d
36.
37. Z
38.
39. a
40. r
41. e
42.
43. t
44. h
45. e
46.
47. s
48. a
49. m
50. e
51.
52. o
53. n
54.
55. t
56. h
57. e
58.
59. t
60. w
61. o
62.
63. s
64. i
65. d
66. e
67. s
68. ,
69.
70. w
71. i
72. t
73. h
74.
75. a
76.
77. p
78. h
79. o
80. t
81. o
82. n
83.
84. e
85. m
86. i
87. t
88. t
89. e
90. d
91. ,
92.
93. i
94. s
95.
96. g
97. a
98. m
99. m
100. a
101.
102. d
103. e
104. c
105. a
106. y
107. .

Question 7: In the chain \( A\xrightarrow{\lambda_1}B\xrightarrow{\lambda_2}C \) where C is stable, with initially only A present, which statement is correct?
(a) The rate of decay of A will first increase and then decrease
(b) If \( \lambda_2>\lambda_1 \), the activity of B will always be higher than that of A
(c) The number of nuclei of B first increases and then decreases
(d) If \( \lambda_1\gg\lambda_2 \), the number of nuclei of C is always less than that of B
Show Answer & Explanation

Answer: (c) The number of nuclei of B first increases and then decreases

Explanation:
1. B is produced from A and itself decays: \( dN_2/dt=\lambda_1N_1-\lambda_2N_2 \) is positive at first and later negative, so N2 rises and then falls.
2. The decay rate of A, \( \lambda_1N_1 \), only decreases.
3. The other two statements are not true in general.

Teacher's Note:
1. A
2. n
3.
4. i
5. n
6. t
7. e
8. r
9. m
10. e
11. d
12. i
13. a
14. t
15. e
16.
17. s
18. p
19. e
20. c
21. i
22. e
23. s
24.
25. i
26. n
27.
28. a
29.
30. d
31. e
32. c
33. a
34. y
35.
36. c
37. h
38. a
39. i
40. n
41.
42. a
43. l
44. w
45. a
46. y
47. s
48.
49. r
50. i
51. s
52. e
53. s
54.
55. t
56. o
57.
58. a
59.
60. m
61. a
62. x
63. i
64. m
65. u
66. m
67.
68. a
69. n
70. d
71.
72. t
73. h
74. e
75. n
76.
77. f
78. a
79. l
80. l
81. s
82. .

Question 8: N atoms of a radioactive element emit n alpha particles per second at an instant. The half-life of the element is:
(a) \( \frac{n}{N} \) s
(b) \( 1.44\frac{n}{N} \) s
(c) \( 0.69\frac{n}{N} \) s
(d) \( 0.69\frac{N}{n} \) s
Show Answer & Explanation

Answer: (d) \( 0.69\frac{N}{n} \) s

Explanation:
1. Activity \( n=\lambda N\Rightarrow\lambda=n/N \).
2. Half-life \( T=\frac{0.693}{\lambda}=0.693\frac{N}{n} \) s.

Teacher's Note:
1. A
2. c
3. t
4. i
5. v
6. i
7. t
8. y
9.
10. d
11. i
12. v
13. i
14. d
15. e
16. d
17.
18. b
19. y
20.
21. t
22. h
23. e
24.
25. n
26. u
27. m
28. b
29. e
30. r
31.
32. o
33. f
34.
35. a
36. t
37. o
38. m
39. s
40.
41. g
42. i
43. v
44. e
45. s
46.
47. t
48. h
49. e
50.
51. d
52. e
53. c
54. a
55. y
56.
57. c
58. o
59. n
60. s
61. t
62. a
63. n
64. t
65. .

Question 9: For uranium nuclei, how does the nuclear mass m vary with the nuclear volume V?
(a) \( m\propto V \) (density is constant)
(b) \( m\propto 1/V \)
(c) \( m\propto\sqrt V \)
(d) \( m\propto V^2 \)
Show Answer & Explanation

Answer: (a) \( m\propto V \) (density is constant)

Explanation:
1. Nuclear matter has nearly the same density in all nuclei, \( \rho\approx 2.3\times10^{17}\ \mathrm{kg\,m^{-3}} \).
2. So \( m=\rho V \) and m is directly proportional to V.

Teacher's Note:
1. T
2. h
3. e
4.
5. n
6. u
7. c
8. l
9. e
10. a
11. r
12.
13. d
14. e
15. n
16. s
17. i
18. t
19. y
20.
21. i
22. s
23.
24. i
25. n
26. d
27. e
28. p
29. e
30. n
31. d
32. e
33. n
34. t
35.
36. o
37. f
38.
39. m
40. a
41. s
42. s
43.
44. n
45. u
46. m
47. b
48. e
49. r
50. .
51.
52. M
53. a
54. s
55. s
56.
57. i
58. s
59.
60. t
61. h
62. e
63. n
64.
65. s
66. i
67. m
68. p
69. l
70. y
71.
72. p
73. r
74. o
75. p
76. o
77. r
78. t
79. i
80. o
81. n
82. a
83. l
84.
85. t
86. o
87.
88. v
89. o
90. l
91. u
92. m
93. e
94. .

Question 10: Consider the nuclear decay \( {}^{236}_{92}U\to{}^{232}_{90}Th+X \) where the uranium nucleus is initially at rest. Given atomic masses U-236 = 236.045562 u, Th-232 = 232.038054 u, He-4 = 4.002603 u, and 1 u = \( 1.5\times10^{-10} \) J, the energy released in this decay is:
(a) \( 3.5\times10^{-8} \) J
(b) \( 7.4\times10^{-13} \) J
(c) \( 4.6\times10^{-12} \) J
(d) \( 6.0\times10^{-10} \) J
Show Answer & Explanation

Answer: (b) \( 7.4\times10^{-13} \) J

Explanation:
1. Mass defect \( =236.045562-232.038054-4.002603=0.004905 \) u.
2. Energy \( =0.004905\times1.5\times10^{-10}=7.4\times10^{-13} \) J.

Teacher's Note:
1. E
2. n
3. e
4. r
5. g
6. y
7.
8. r
9. e
10. l
11. e
12. a
13. s
14. e
15. d
16.
17. e
18. q
19. u
20. a
21. l
22. s
23.
24. t
25. h
26. e
27.
28. m
29. a
30. s
31. s
32.
33. d
34. e
35. f
36. e
37. c
38. t
39.
40. t
41. i
42. m
43. e
44. s
45.
46. t
47. h
48. e
49.
50. e
51. n
52. e
53. r
54. g
55. y
56.
57. e
58. q
59. u
60. i
61. v
62. a
63. l
64. e
65. n
66. t
67.
68. o
69. f
70.
71. o
72. n
73. e
74.
75. a
76. t
77. o
78. m
79. i
80. c
81.
82. m
83. a
84. s
85. s
86.
87. u
88. n
89. i
90. t
91. .

Question 11: Two identical samples P and Q of a radioactive substance having mean life T are observed to have activities \( A_P \) and \( A_Q \) at the time of observation. If P is older than Q, the difference in their ages is:
(a) \( T\ln\left(\frac{A_P}{A_Q}\right) \)
(b) \( \frac1T\ln\left(\frac{A_P}{A_Q}\right) \)
(c) \( T\ln\left(\frac{A_Q}{A_P}\right) \)
(d) \( T\left(\frac{A_P}{A_Q}\right) \)
Show Answer & Explanation

Answer: (c) \( T\ln\left(\frac{A_Q}{A_P}\right) \)

Explanation:
1. \( A_P=A_0e^{-t_P/T} \) and \( A_Q=A_0e^{-t_Q/T} \).
2. \( \frac{A_Q}{A_P}=e^{(t_P-t_Q)/T}\Rightarrow t_P-t_Q=T\ln\frac{A_Q}{A_P} \).

Teacher's Note:
1. T
2. a
3. k
4. e
5.
6. t
7. h
8. e
9.
10. r
11. a
12. t
13. i
14. o
15.
16. o
17. f
18.
19. t
20. h
21. e
22.
23. t
24. w
25. o
26.
27. e
28. x
29. p
30. o
31. n
32. e
33. n
34. t
35. i
36. a
37. l
38. s
39.
40. a
41. n
42. d
43.
44. s
45. o
46. l
47. v
48. e
49.
50. f
51. o
52. r
53.
54. t
55. h
56. e
57.
58. d
59. i
60. f
61. f
62. e
63. r
64. e
65. n
66. c
67. e
68.
69. i
70. n
71.
72. t
73. i
74. m
75. e
76. s
77. .

Question 12: A box contained an alloy of equal parts by weight of two radioactive metals A and B with half-lives 12 years and 18 years. When opened it contained 0.53 kg of A and 2.20 kg of B. The age of the alloy is \( M\times10+n \) years, where n is a single digit. The value of M - n is:
(a) 4
(b) 2
(c) 5
(d) 3
Show Answer & Explanation

Answer: (d) 3

Explanation:
1. Equal initial masses, so \( \frac{m_A}{m_B}=2^{-t/12+t/18} \).
2. \( \frac{0.53}{2.20}=2^{-t/36}\Rightarrow t=36\log_2\frac{2.20}{0.53}=36\times2.05=73.9\approx74 \) years.
3. So M = 7, n = 4 and M - n = 3.

Teacher's Note:
1. E
2. q
3. u
4. a
5. l
6.
7. i
8. n
9. i
10. t
11. i
12. a
13. l
14.
15. m
16. a
17. s
18. s
19. e
20. s
21.
22. m
23. e
24. a
25. n
26.
27. t
28. h
29. e
30.
31. r
32. a
33. t
34. i
35. o
36.
37. o
38. f
39.
40. f
41. i
42. n
43. a
44. l
45.
46. m
47. a
48. s
49. s
50. e
51. s
52.
53. d
54. e
55. p
56. e
57. n
58. d
59. s
60.
61. o
62. n
63. l
64. y
65.
66. o
67. n
68.
69. t
70. h
71. e
72.
73. d
74. i
75. f
76. f
77. e
78. r
79. e
80. n
81. c
82. e
83.
84. o
85. f
86.
87. t
88. h
89. e
90.
91. t
92. w
93. o
94.
95. d
96. e
97. c
98. a
99. y
100.
101. f
102. a
103. c
104. t
105. o
106. r
107. s
108. .

Question 13: A point source emits alpha particles and a receptor of area 1 cm\( ^2 \) is placed 1 m away. The receptor records a rate of 50000 counts per second. The source contains \( N_0=3.0\times10^{16} \) active nuclei and emits uniformly in all directions, the particles falling nearly normally on the window. If the decay constant is \( 3n\times10^{-(n+1)}\ \mathrm{s^{-1}} \), the value of n is:
(a) 7
(b) 8
(c) 6
(d) 9
Show Answer & Explanation

Answer: (a) 7

Explanation:
1. Fraction reaching the receptor \( =\frac{10^{-4}}{4\pi(1)^2} \).
2. Counts \( =\lambda N_0\frac{10^{-4}}{4\pi}=5\times10^4\Rightarrow\lambda=\frac{4\pi\times5\times10^4}{3\times10^{16}\times10^{-4}}=2.1\times10^{-7}\ \mathrm{s^{-1}} \).
3. \( 3n\times10^{-(n+1)} \) equals \( 2.1\times10^{-7} \) for n = 7 (\( 21\times10^{-8} \)).

Teacher's Note:
1. T
2. h
3. e
4.
5. d
6. e
7. t
8. e
9. c
10. t
11. o
12. r
13.
14. s
15. u
16. b
17. t
18. e
19. n
20. d
21. s
22.
23. a
24.
25. f
26. r
27. a
28. c
29. t
30. i
31. o
32. n
33.
34. (
35. a
36. r
37. e
38. a
39.
40. d
41. i
42. v
43. i
44. d
45. e
46. d
47.
48. b
49. y
50.
51. 4
52.
53. p
54. i
55.
56. r
57.
58. s
59. q
60. u
61. a
62. r
63. e
64. d
65. )
66.
67. o
68. f
69.
70. t
71. h
72. e
73.
74. e
75. m
76. i
77. s
78. s
79. i
80. o
81. n
82. ,
83.
84. s
85. o
86.
87. t
88. h
89. e
90.
91. a
92. c
93. t
94. i
95. v
96. i
97. t
98. y
99.
100. i
101. s
102.
103. s
104. c
105. a
106. l
107. e
108. d
109.
110. b
111. y
112.
113. t
114. h
115. a
116. t
117.
118. f
119. r
120. a
121. c
122. t
123. i
124. o
125. n
126. .

Question 14: A charged capacitor of capacitance C is discharged through a resistance R. A radioactive sample decays with average life \( \tau \). The value of R for which the ratio of the electrostatic energy stored in the capacitor to the activity of the sample is independent of time is:
(a) \( \frac{\tau}{C} \)
(b) \( \frac{2\tau}{C} \)
(c) \( \frac{\tau}{2C} \)
(d) \( \frac{3\tau}{2C} \)
Show Answer & Explanation

Answer: (b) \( \frac{2\tau}{C} \)

Explanation:
1. Energy stored \( U=U_0e^{-2t/RC} \) (charge falls as \( e^{-t/RC} \)); activity \( A=A_0e^{-t/\tau} \).
2. For U/A to be constant: \( \frac{2}{RC}=\frac1\tau\Rightarrow R=\frac{2\tau}{C} \).

Teacher's Note:
1. E
2. n
3. e
4. r
5. g
6. y
7.
8. g
9. o
10. e
11. s
12.
13. a
14. s
15.
16. t
17. h
18. e
19.
20. s
21. q
22. u
23. a
24. r
25. e
26.
27. o
28. f
29.
30. c
31. h
32. a
33. r
34. g
35. e
36. ,
37.
38. s
39. o
40.
41. i
42. t
43.
44. d
45. e
46. c
47. a
48. y
49. s
50.
51. t
52. w
53. i
54. c
55. e
56.
57. a
58. s
59.
60. f
61. a
62. s
63. t
64.
65. a
66. s
67.
68. t
69. h
70. e
71.
72. c
73. h
74. a
75. r
76. g
77. e
78.
79. d
80. o
81. e
82. s
83. .

Question 15: About how many beta particles are emitted in one hour by 1.0 microgram of \( {}^{24}_{11}\mathrm{Na} \) (half-life 15 h; take \( e^{-0.693/15}=0.955 \) and \( N_A=6\times10^{23} \))?
(a) \( 2.5\times10^{16} \)
(b) \( 1.1\times10^{18} \)
(c) \( 1.1\times10^{15} \)
(d) \( 2.5\times10^{13} \)
Show Answer & Explanation

Answer: (c) \( 1.1\times10^{15} \)

Explanation:
1. Number of atoms \( N_0=\frac{10^{-6}}{24}\times6\times10^{23}=2.5\times10^{16} \).
2. Decayed in 1 h \( =N_0(1-0.955)=1.1\times10^{15} \).

Teacher's Note:
1. E
2. a
3. c
4. h
5.
6. d
7. e
8. c
9. a
10. y
11.
12. o
13. f
14.
15. s
16. o
17. d
18. i
19. u
20. m
21. -
22. 2
23. 4
24.
25. e
26. m
27. i
28. t
29. s
30.
31. o
32. n
33. e
34.
35. b
36. e
37. t
38. a
39.
40. p
41. a
42. r
43. t
44. i
45. c
46. l
47. e
48. ,
49.
50. s
51. o
52.
53. t
54. h
55. e
56.
57. n
58. u
59. m
60. b
61. e
62. r
63.
64. d
65. e
66. c
67. a
68. y
69. e
70. d
71.
72. e
73. q
74. u
75. a
76. l
77. s
78.
79. t
80. h
81. e
82.
83. n
84. u
85. m
86. b
87. e
88. r
89.
90. e
91. m
92. i
93. t
94. t
95. e
96. d
97. .

Question 16: A nucleus \( {}^A_Z X \) emits one alpha particle and then one beta (negative) particle in succession. Which of the following are true for the daughter nucleus? (A) it has A - 4 nucleons, (B) it has 4 nucleons, (C) it has A - Z - 3 neutrons, (D) it has Z - 2 protons. Select the correct combination.
(a) B and D only
(b) A and D only
(c) B and C only
(d) A and C only
Show Answer & Explanation

Answer: (d) A and C only

Explanation:
1. After the alpha: mass number A - 4, charge Z - 2. After the beta-minus: mass number A - 4, charge Z - 1.
2. Neutrons \( =(A-4)-(Z-1)=A-Z-3 \).
3. So (A) and (C) are true, (B) and (D) are false.

Teacher's Note:
1. B
2. e
3. t
4. a
5. -
6. m
7. i
8. n
9. u
10. s
11.
12. r
13. a
14. i
15. s
16. e
17. s
18.
19. Z
20.
21. b
22. y
23.
24. o
25. n
26. e
27.
28. w
29. i
30. t
31. h
32. o
33. u
34. t
35.
36. c
37. h
38. a
39. n
40. g
41. i
42. n
43. g
44.
45. A
46. .

Question 17: Ninety percent of a radioactive sample is left after a time interval t. The percentage of the initial sample that will disintegrate in an interval 2t is:
(a) 19%
(b) 38%
(c) 9%
(d) 62%
Show Answer & Explanation

Answer: (a) 19%

Explanation:
1. Fraction left after t is 0.9, so after 2t it is \( 0.9^2=0.81 \).
2. Disintegrated \( =1-0.81=0.19 \), i.e. 19 percent.

Teacher's Note:
1. F
2. r
3. a
4. c
5. t
6. i
7. o
8. n
9. s
10.
11. l
12. e
13. f
14. t
15.
16. m
17. u
18. l
19. t
20. i
21. p
22. l
23. y
24.
25. f
26. o
27. r
28.
29. s
30. u
31. c
32. c
33. e
34. s
35. s
36. i
37. v
38. e
39.
40. e
41. q
42. u
43. a
44. l
45.
46. i
47. n
48. t
49. e
50. r
51. v
52. a
53. l
54. s
55. .

Question 18: 10 g of \( {}^{57}_{27}\mathrm{Co} \) is kept in an open container and decays by beta emission with half-life 270 days. The weight of the material left in the container after 540 days is very nearly:
(a) 10 g
(b) 2.5 g
(c) 7.5 g
(d) 5 g
Show Answer & Explanation

Answer: (b) 2.5 g

Explanation:
1. 540 days = 2 half-lives, so the cobalt left is \( 10\times\tfrac14=2.5 \) g.
2. The cobalt-57 is what remains; the beta particles and the daughter nuclei are not counted as cobalt.

Teacher's Note:
1. N
2. u
3. m
4. b
5. e
6. r
7.
8. o
9. f
10.
11. h
12. a
13. l
14. f
15. -
16. l
17. i
18. v
19. e
20. s
21.
22. =
23.
24. e
25. l
26. a
27. p
28. s
29. e
30. d
31.
32. t
33. i
34. m
35. e
36.
37. d
38. i
39. v
40. i
41. d
42. e
43. d
44.
45. b
46. y
47.
48. h
49. a
50. l
51. f
52. -
53. l
54. i
55. f
56. e
57. ;
58.
59. t
60. h
61. e
62.
63. a
64. m
65. o
66. u
67. n
68. t
69.
70. h
71. a
72. l
73. v
74. e
75. s
76.
77. e
78. a
79. c
80. h
81.
82. t
83. i
84. m
85. e
86. .

Question 19: The masses of two isobars \( {}^{64}_{29}\mathrm{Cu} \) and \( {}^{64}_{30}\mathrm{Zn} \) are 63.9298 u and 63.9292 u respectively. It can be concluded that:
(a) both the isobars are stable
(b) Zn-64 is radioactive, decaying to Cu-64 through beta decay
(c) Cu-64 is radioactive, decaying to Zn-64 through beta decay
(d) Cu-64 is radioactive, decaying to Zn-64 through gamma decay
Show Answer & Explanation

Answer: (c) Cu-64 is radioactive, decaying to Zn-64 through beta decay

Explanation:
1. Cu-64 is heavier than Zn-64 by 0.0006 u, so it can decay to Zn-64.
2. Z increases from 29 to 30 at constant A: that is beta-minus decay.

Teacher's Note:
1. A
2.
3. n
4. u
5. c
6. l
7. e
8. u
9. s
10.
11. c
12. a
13. n
14.
15. d
16. e
17. c
18. a
19. y
20.
21. i
22. n
23. t
24. o
25.
26. a
27. n
28.
29. i
30. s
31. o
32. b
33. a
34. r
35.
36. o
37. n
38. l
39. y
40.
41. i
42. f
43.
44. t
45. h
46. e
47.
48. d
49. a
50. u
51. g
52. h
53. t
54. e
55. r
56.
57. h
58. a
59. s
60.
61. t
62. h
63. e
64.
65. l
66. o
67. w
68. e
69. r
70.
71. m
72. a
73. s
74. s
75. .

Question 20: Deuterium fuses by \( 2\,{}^2_1\mathrm{H}\to{}^4_2\mathrm{He}+Q \) (\( {}^4He=4.002603 \) u, \( {}^2H=2.014102 \) u). To generate 50 MW of power at 30 percent efficiency, the mass of deuterium consumed per second is nearly:
(a) \( 1.5\times10^{-4} \) g
(b) \( 2.9\times10^{-7} \) g
(c) \( 5.8\times10^{-4} \) g
(d) \( 2.9\times10^{-4} \) g
Show Answer & Explanation

Answer: (d) \( 2.9\times10^{-4} \) g

Explanation:
1. Q \( =(2\times2.014102-4.002603)\times931=23.8 \) MeV per fusion.
2. Required thermal power \( =50/0.3=167 \) MW, so fusions per second \( =\frac{1.67\times10^8}{23.8\times1.6\times10^{-13}}=4.4\times10^{19} \).
3. Each fusion uses 2 deuterons: mass \( =\frac{8.7\times10^{19}\times2.014}{6.02\times10^{23}}=2.9\times10^{-4} \) g/s.

Teacher's Note:
1. E
2. f
3. f
4. i
5. c
6. i
7. e
8. n
9. c
10. y
11.
12. r
13. a
14. i
15. s
16. e
17. s
18.
19. t
20. h
21. e
22.
23. r
24. e
25. q
26. u
27. i
28. r
29. e
30. d
31.
32. e
33. n
34. e
35. r
36. g
37. y
38.
39. i
40. n
41. p
42. u
43. t
44. :
45.
46. o
47. u
48. t
49. p
50. u
51. t
52.
53. d
54. i
55. v
56. i
57. d
58. e
59. d
60.
61. b
62. y
63.
64. e
65. f
66. f
67. i
68. c
69. i
70. e
71. n
72. c
73. y
74. .

Question 21: Assuming about 20 MeV of energy is released per fusion reaction \( {}^2_1\mathrm{H}+{}^3_1\mathrm{H}\to{}^1_0n+{}^4_2\mathrm{He} \), the mass of \( {}^2_1H \) consumed in one day in a fusion reactor of power 1 MW would be approximately:
(a) 0.1 g
(b) 0.01 g
(c) 1 g
(d) 10 g
Show Answer & Explanation

Answer: (a) 0.1 g

Explanation:
1. Reactions per day \( =\frac{10^6\times86400}{20\times1.6\times10^{-13}}=2.7\times10^{22} \).
2. Each reaction uses one deuteron: mass \( =\frac{2.7\times10^{22}\times2}{6.02\times10^{23}}\approx0.09 \) g, about 0.1 g.

Teacher's Note:
1. C
2. o
3. n
4. v
5. e
6. r
7. t
8.
9. p
10. o
11. w
12. e
13. r
14.
15. t
16. o
17.
18. r
19. e
20. a
21. c
22. t
23. i
24. o
25. n
26. s
27.
28. p
29. e
30. r
31.
32. s
33. e
34. c
35. o
36. n
37. d
38. ,
39.
40. t
41. h
42. e
43. n
44.
45. t
46. o
47.
48. n
49. u
50. m
51. b
52. e
53. r
54.
55. o
56. f
57.
58. d
59. e
60. u
61. t
62. e
63. r
64. i
65. u
66. m
67.
68. a
69. t
70. o
71. m
72. s
73. ,
74.
75. t
76. h
77. e
78. n
79.
80. t
81. o
82.
83. g
84. r
85. a
86. m
87. s
88.
89. u
90. s
91. i
92. n
93. g
94.
95. A
96. v
97. o
98. g
99. a
100. d
101. r
102. o
103. '
104. s
105.
106. n
107. u
108. m
109. b
110. e
111. r
112. .

Question 22: In the chain \( A\xrightarrow{\lambda}B\xrightarrow{2\lambda}C \) with initially only A present (\( N_1,N_2,N_3 \) are the numbers of A, B, C at time t), the ratio \( N_1:N_2 \) at the instant when \( N_2 \) is maximum is:
(a) 1/2
(b) 2
(c) \( \frac{\ln 2}{2} \)
(d) This is never possible
Show Answer & Explanation

Answer: (b) 2

Explanation:
1. N2 is maximum when \( dN_2/dt=0 \).
2. \( \frac{dN_2}{dt}=\lambda N_1-2\lambda N_2=0\Rightarrow N_1=2N_2 \).
3. Hence \( N_1:N_2=2 \).

Teacher's Note:
1. A
2. t
3.
4. t
5. h
6. e
7.
8. m
9. a
10. x
11. i
12. m
13. u
14. m
15.
16. o
17. f
18.
19. t
20. h
21. e
22.
23. i
24. n
25. t
26. e
27. r
28. m
29. e
30. d
31. i
32. a
33. t
34. e
35.
36. s
37. p
38. e
39. c
40. i
41. e
42. s
43.
44. i
45. t
46. s
47.
48. p
49. r
50. o
51. d
52. u
53. c
54. t
55. i
56. o
57. n
58.
59. r
60. a
61. t
62. e
63.
64. e
65. q
66. u
67. a
68. l
69. s
70.
71. i
72. t
73. s
74.
75. d
76. e
77. c
78. a
79. y
80.
81. r
82. a
83. t
84. e
85. .

Question 23: Protons and singly ionised atoms of U-235 and U-238 are passed in turn through a velocity selector and then enter a uniform magnetic field. The protons describe semicircles of radius 10 mm. The separation between the ions of U-235 and U-238 after describing a semicircle is:
(a) 30 mm
(b) 2350 mm
(c) 60 mm
(d) 2380 mm
Show Answer & Explanation

Answer: (c) 60 mm

Explanation:
1. Radius \( r=\frac{mv}{qB}\propto m \) for the same q, v, B; so r for U-235 is 2350 mm and for U-238 is 2380 mm (taking mass numbers as the mass ratio to the proton).
2. After a semicircle the ions are at distance \( 2r \) from the entry slit, so the separation is \( 2(2380-2350)=60 \) mm.

Teacher's Note:
1. T
2. h
3. e
4.
5. i
6. o
7. n
8. s
9.
10. l
11. a
12. n
13. d
14.
15. a
16. t
17.
18. o
19. n
20. e
21.
22. d
23. i
24. a
25. m
26. e
27. t
28. e
29. r
30.
31. f
32. r
33. o
34. m
35.
36. t
37. h
38. e
39.
40. s
41. l
42. i
43. t
44. ,
45.
46. s
47. o
48.
49. t
50. h
51. e
52.
53. s
54. e
55. p
56. a
57. r
58. a
59. t
60. i
61. o
62. n
63.
64. i
65. s
66.
67. t
68. w
69. i
70. c
71. e
72.
73. t
74. h
75. e
76.
77. d
78. i
79. f
80. f
81. e
82. r
83. e
84. n
85. c
86. e
87.
88. i
89. n
90.
91. r
92. a
93. d
94. i
95. i
96. .

Free study material for Physics

Multiple Choice Questions (MCQs) for JEE Physics Nuclei

Chapter MCQs with Answers for JEE Physics

Test your conceptual understanding of Nuclei with these targeted multiple-choice questions. Designed in alignment with the latest JEE curriculum for JEE Physics, these problem sets build accuracy and prepare students for objective exams.

Expert Practice Material for JEE Physics

Cross-reference your completed choices with comprehensive NCERT solutions for JEE Physics to ensure absolute clarity across all sub-topics in this chapter.

Complete Your Chapter Revision

Follow up your worksheet practice by attempting the interactive online Physics MCQ test for this chapter to evaluate your execution speed. All platform resources are free to access.

FAQs

Where can I access latest JEE Physics Nuclei MCQs Set 21?

You can get most exhaustive JEE Physics Nuclei MCQs Set 21 for free on StudiesToday.com. These MCQs for JEE Physics are updated for the 2026-27 academic session as per JEE examination standards.

Are Assertion-Reasoning and Case-Study MCQs included in the Physics JEE material?

Yes, our JEE Physics Nuclei MCQs Set 21 include the latest type of questions, such as Assertion-Reasoning and Case-based MCQs. 50% of the JEE paper is now competency-based.

How do practicing Physics MCQs help in scoring full marks in JEE exams?

By solving our JEE Physics Nuclei MCQs Set 21, JEE students can improve their accuracy and speed which is important as objective questions provide a chance to secure 100% marks in the Physics.

Do you provide answers and explanations for JEE Physics Nuclei MCQs Set 21?

Yes, Physics MCQs for JEE have answer key and brief explanations to help students understand logic behind the correct option as its important for 2026 competency-focused JEE exams.

Can I practice these Physics JEE MCQs online?

Yes, you can also access online interactive tests for JEE Physics Nuclei MCQs Set 21 on StudiesToday.com as they provide instant answers and score to help you track your progress in Physics.