The molar conductivity of a $0.10\mathrm{M}$ solution of a weak monobasic acid is $7.8\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$ and its limiting molar conductivity is $390\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$. The degree of dissociation of the acid in this solution is

1. A$0.02$
2. B$0.2$
3. C$0.002$
4. D$50$