The molar conductivity of aqueous solution of a weak acid HA is $200Sc{m}^{2}mo{l}^{-1}$ and its  $P^H$ is 4. What is the value of HA at  ${25}^{0}C P^{ka}$ 
(Given ${\lambda }_m^0\left(NaA\right)=100Sc{m}^{2}mo{l}^{-1},{\lambda }_m^0\left(HCl\right)=425Sc{m}^{2}mo{l}^{-1},{\lambda }_m^0\left(NaCl\right)=125Sc{m}^{2}mo{l}^{-1}$)