Consider a free neutron in space. Which of the following can we NOT say about it?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → It decays into an electron, a proton and a neutrino.
Option (1) It is unstable. — True about a free neutron. A free neutron, unlike a free proton, is unstable. It is stable only inside a nucleus.
Option (2) It decays into an electron, a proton and a neutrino. — Not true about a free neutron. The third particle given out is an antineutrino. A free neutron does not give out a neutrino.
Option (3) It has a mean life of about 1000 s. — True about a free neutron. A free neutron survives on average for about 1000 s before it decays.
Option (4) It decays into an electron, a proton and an antineutrino. — True about a free neutron. These are the three particles into which a free neutron decays.
NCERT (2026-27):
Atomic Masses and Composition of Nucleus – “A free neutron, unlike a free proton, is unstable. It decays into a proton, an electron and a antineutrino (another elementary particle), and has a mean life of about 1000s. It is, however, stable inside the nucleus.”