$=1.29 \times 100 m^{-1}$
Given, $R=520 \Omega, C=0.2 M, \mu$ (molar conductivity) $=?$
$\mu=\kappa \times V \quad\left(\kappa \text { can be calculated as } \kappa=\frac{1}{R}\left(\frac{1}{a}\right)\right.$
now cell constant is known.
Hence, $\mu=\frac{1}{520} \times 129 \times \frac{1000}{0.2} \times 10^{-6} \mathrm{m}^{3}$
$=12.4 \times 10^{-4} \mathrm{Sm}^{2} \mathrm{mol}^{-1}$
$H_3PO_4 + OH^- \rightarrow H_2PO_4^- + H_2O$ ;
$H_3PO_4 + 2OH^- \rightarrow HPO_4^{2-} + 2H_2O$ ;
$H_3PO_4 + 3OH^- \rightarrow PO_4^{3-} + 3H_2O$