C

To derive the radius of the circular path of an electron in a magnetic field, we use the formula:
$$ r = \frac{mv}{qB} $$
where:
- $r$ is the radius of the path,
- $m$ is the mass of the electron,
- $v$ is the velocity of the electron,
- $q$ is the charge of the electron,
- $B$ is the magnetic field strength.
Since electrons have a specific mass (approximately $9.11 \times 10^{-31}$ kg) and charge (approximately $1.6 \times 10^{-19}$ C), by substituting these values and solving for $r$, we would find that Option C correctly represents this relationship.