Verified Solution • 2025–26 Session moderate

QPages 441-442: Q3: HC Verma: Concepts of Physics - Volume 2 The Nucleus Pages 441-442: Q3 Solution: A free neutron decays to a proton but a free proton does not…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often choose the charge‑or composition‑based options, overlooking that a particle can only decay if its rest mass exceeds the total rest mass of the decay products. Remember that a free neutron ($m_n\approx 939.6\,\text{MeV}$) can beta‑decay to a proton ($m_p\approx 938.3\,\text{MeV}$) plus an electron and an antineutrino because the mass excess provides the kinetic energy; a proton lacks this excess, so it cannot decay to a neutron.

A free neutron decays to a proton but a free proton does not decay to a neutron. This is because

Multiple Choice Options

  • A neutron is a composite particle made of a proton and an electron whereas proton is a fundamental particle
  • B neutron is an uncharged particle whereas proton is a charged particle
  • C neutron has large rest mass than the proton
  • D weak forces can operate in a neutron but not in a proton

Step-by-Step Verified Solution

**Answer:** (c) neutron has large rest mass than the proton. **Step-by-Step Explanation:** A free neutron decays to a proton because the neutron has greater rest mass than the proton.

All Questions in this Chapter

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