What is the $\mathrm{SI}$ unit of conductivity?
 

The limiting molar conductivities $\mathrm{\Lambda }º$ for $\mathrm{NaCl}, \mathrm{KBr} \mathrm{and} \mathrm{KCl} \mathrm{are}\mathrm{126, 152 }\mathrm{and} \mathrm{150 }\mathrm{S} {\mathrm{cm}}^{\mathrm{2}} {\mathrm{mol}}^{-1}$ respectively. The $\mathrm{\Lambda }º$ for $\mathrm{NaBr}$ is ______.

At $25°\mathrm{C}$, the molar conductance of $0.007 \mathrm{M}$ hydrofluoric acid is $\mathrm{150 }\mathrm{mho} {\mathrm{cm}}^{\mathrm{2}} {\mathrm{mol}}^{\mathrm{-1}}$ and ${\mathrm{\Lambda }}^{°}$  = $\mathrm{500 }\mathrm{mho} {\mathrm{cm}}^{\mathrm{2}} {\mathrm{mol}}^{\mathrm{-1}}$. The value of the dissociation constant of the acid at the given concentration at $25º\mathrm{C}$ is _____.