At constant volume and temperature conditions, the rates of diffusion $D_{A}$ and $D_{B}$ of gases $A$ and $B$ having densities $\rho_{A}$ and $\rho_{B}$ are related by the expression:
(a) $\mathrm{D}_{\mathrm{A}}=\left[\mathrm{D}_{\mathrm{B}} \rho_{A} / \rho_{\mathrm{B}}\right]^{1 / 2}$
(b) $\mathrm{D}_{\mathrm{A}}=\left[\mathrm{D}_{\mathrm{B}} \rho_{\mathrm{B}} / \rho_{\mathrm{A}}\right]^{1 / 2}$
(c) $\mathrm{D}_{\mathrm{A}}=\mathrm{D}_{\mathrm{B}}\left[\rho_{A} / \rho_{\mathrm{B}}\right]^{1 / 2}$
(d) $\mathrm{D}_{\mathrm{A}}=\mathrm{D}_{\mathrm{B}}\left[\rho_{\mathrm{B}} / \rho_{\mathrm{A}}\right]^{1 / 2}$