When a beta particle is given out, the atomic number of parent atoms?
A. Increase by unity
B. Decreases by unity
C. Remains the same
D. Is halved

Hint: Radioactivity, the process through which every atom which has unbalanced forces in the nucleus trends to disassociate into stable atoms. The result of these forces causes the atom to emit an excess of proton or neutron, whatever is the cause of instability of atoms. The decay of atoms happens in several ways. One of them is beta decay.

Complete answer:
Nucleus of atoms accommodates various particles in it through a special short range force. Which is limited to the range of nucleus only is the strong nuclear force. The beta particles originate through the nucleus when an atom undergoes a radioactivity decay. Beta particles are similar to electrons in terms of mass. They can be positive (positron) or negatively charged.

Beta emission is of two types:
-\[{\beta ^ + }\] decay: The atom decays into a proton and neutron, positron, neutrino along with an atom of having the same mass number but atomic number decreased by one.
\[{}_Z^AX \to {}_{Z - 1}^AY + {}_{ + 1}^0e + v\]
-\[{\beta ^ - }\] decay: The atom decays a neutron into proton, anti-neutrino and \[{\beta ^ - }\]particle (electron)along with an atom of having the same mass number but atomic number increased by one.
\[{}_Z^AX \to {}_{Z + 1}^AY + {}_{ - 1}^0e + \overline v \]

Thus, options A and option B both are correct options.

Note:Beta particles due to their small mass and size acquire high energy, speed.They have many applications in our day to day lives. They are used to create different thickness of papers by the amount of radiation they absorb. Beta particles are used to destroy cancer causing cells and also treats the eye conditions.