Q1(b). Carbon isotopes and stability

Answer in brief

Carbon-14 is neutron rich and undergoes β⁻ decay to stable nitrogen-14; carbon-12 lies in the stable light-nucleus region.

Key points

• ¹²₆C has six protons and six neutrons. For light nuclei a neutron/proton ratio near one is usually favourable; carbon-12 is even–even and stable.
• ¹⁴₆C has eight neutrons and six protons. A neutron converts into a proton, reducing the neutron excess while preserving mass number.
• The decay is ¹⁴₆C → ¹⁴₇N+e⁻+ν̄ₑ. Nitrogen-14 has seven protons and seven neutrons. Decay is possible because the full mass-energy balance is favourable.