Beta Decay

In beta-minus decay, described in NCERT, a neutron inside the nucleus converts into a proton, and to conserve charge and lepton number it ejects an electron together with an antineutrino, written $n\to p+e^{-}+\bar{\nu }$. The nuclear charge rises by one while the mass number stays the same. The option of a positron and neutrino describes beta-plus decay, which occurs in proton-rich nuclei and is the opposite process, so it is wrong here. The option of an alpha particle and a photon is wrong because those belong to alpha and gamma emission, not beta decay. The option of a proton and an electron is wrong because the proton remains bound in the nucleus; only the electron and antineutrino escape. As stated in NCERT Class 12, Chapter 13 (Nuclei), the antineutrino was postulated by Pauli to account for the continuous energy spectrum of the emitted electrons, since a two-body decay would give the electron a single fixed energy. The shared energy between the electron and antineutrino explains why beta particles emerge with a range of energies up to a maximum. A consistency check: charge balances since a neutral neutron yields a positive proton, a negative electron, and a neutral antineutrino, summing to zero net change in emitted charge and raising $Z$ by one.