Explanation : (B) Atoms of different elements having same mass numbers but different atomic numbers are called isobars. Isobar is formed due to beta emission of a radioactive element.
Explanation : (D) Hydrogen has three main isotopes, there are protium (1H) deuterium (2H) and tritium (3H). Protium and deuterium are stable while tritium is radioactive and has a half-life of about 12 years