The correct option is A the nucleus of atom.
The beta particle β, which may be either negatively charged (negatrons) or positively charged (positrons), originates from the nucleus of an atom.
A beta particle is emitted from the nucleus of an atom during radioactive decay.
n→p+e−1 (β particle)+¯v
Beta decay occurs in isotopes which are neutron rich - have a lot more neutrons in their nucleus than protons.