JEE Main 2024 · 4 April · morning · Single correct · +4 / −1

Which of the following nuclear fragments corresponding to nuclear fission between neutron ( ₀¹ n) and uranium isotope ( ₉₂²³⁵ U) is correct :

  1. (a) ₅₆¹⁴⁰ Xe+ ₃₈⁹⁴ Sr+3 ₀¹ n
  2. (b) ₅₁¹⁵³ Sb+ ₄₁⁹⁹ Nb+3 ₀¹ n
  3. (c) ₅₆¹⁴⁴ Ba+ ₃₆⁸⁹ Kr+4 ₀¹ n
  4. (d) ₅₆¹⁴⁴ Ba+ ₃₆⁸⁹ Kr+3 ₀¹ n
Answer and solution

Answer (d) ₅₆¹⁴⁴ Ba+ ₃₆⁸⁹ Kr+3 ₀¹ n

Solution

Physics sir · 2 steps

Ignore the element names: add up A and Z on both sides and pick the option that balances.

  1. Left side. The neutron brings A = 1, Z = 0 and uranium brings A = 235, Z = 92. So the products must add up to A = 236 and Z = 92.

    ₀¹n + ₉₂²³⁵U → ₅₆¹⁴⁴Ba + ₃₆⁸⁹Kr + 3 ₀¹n

    OptionSum of A (need 236)Sum of Z (need 92)Verdict
    (a)140 + 94 + 3 = 23756 + 38 = 94both fail
    (b)153 + 99 + 3 = 25551 + 41 = 92A fails
    (c)144 + 89 + 4 = 23756 + 36 = 92A fails
    (d)144 + 89 + 3 = 23656 + 36 = 92balanced
  2. So. Only (d) conserves both the nucleon number and the charge, so it is the correct set of fission fragments.

The idea to keep. In any nuclear reaction, the mass numbers and the atomic numbers must each add up to the same total on both sides. Count the incoming neutron and every emitted neutron.

Answer from the NTA final answer key. Solution by PrepWiser.

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Asked about 110 times in JEE Main since 2020. This question is from 2024.