The gyro magnetic ratio is the ratio of the magnetic moment (\( \mu \)) to the angular momentum (\( L \)) of a particle. It is defined as:
\[
\gamma = \frac{\mu}{L}
\]
For a charged particle moving in a magnetic field, the magnetic moment is related to the charge (\( q \)) and mass (\( m \)) of the particle. The gyro magnetic ratio is given by:
\[
\gamma = \frac{q}{m}
\]
This ratio determines how the particle behaves in the presence of a magnetic field.
Thus, the correct answer is \( \frac{q}{m} \).