Step 1: The equation connects a bulk, measurable property (the relative permittivity $\epsilon_r$) with an atomic-scale property (the polarizability $\alpha$) and the number density $n$ of dipoles.
Step 2: Such a micro-to-macro dielectric bridge is derived by inserting the Lorentz local field $E_{\text{loc}} = E + P/3\epsilon_0$ into the definition of polarization, which produces the factor $(\epsilon_r+2)$ in the denominator.
Step 3: The resulting expression $\dfrac{\epsilon_r-1}{\epsilon_r+2} = \dfrac{n\alpha}{3\epsilon_0}$ is the well-known Clausius-Mossotti relation for non-polar dielectrics.
Step 4: Debye's equation extends this to polar molecules by adding an orientational term, but the bare polarizability form written here is specifically Clausius-Mossotti. Hence option (B) is correct.\[\boxed{\text{Clausius-Mossotti}}\]