A. The mass number of the original nucleus changes.
An atom undergoes β-decay because it is unstable.
When it decays,
C. The original nucleus approaches greater stability
D. Energy is released.
A typical β-decay reaction is
#""_6^14"C" → ""_7^14"N" +color(white)(l) _text(-1)^0"e" + bar(ν)_e#
B. The atomic number of the original nucleus changes (from 6 to 7)
A. The mass number of the original nucleus stays the same (at 14).
Therefore A is the incorrect statement.