For the radioactive nuclei that undergo either $a$ or $\beta$ decay, which one of the following cannot occur?

• A

  Isobar of original nucleus is produced
• Correct answer
  B

  Isotope of the original nucleus is produced
• C

  Nuclei with higher atomic number than that of the original nucleus is produced
• D

  Nuclei with lower atomic number than that of the original nucleus is produced

Hence, the correct answer is option: 'B'.