1. Use Kohlrausch’s law of independent migration of ions

For an electrolyte, the molar conductivity at infinite dilution is the sum of the molar ionic conductivities of the ions, each multiplied by its stoichiometric coefficient:

$\Lambda_m^\circ = \nu_+ \lambda_+^\circ + \nu_- \lambda_-^\circ$

2. Identify the electrolyte type

The cation is divalent and the anion is also divalent.

So the electrolyte formed is of type:

$\text{M}^{2+} + \text{X}^{2-} \rightarrow \text{MX}$

Thus, the stoichiometric coefficients are:

$\nu_+ = 1, \qquad \nu_- = 1$

3. Substitute the given ionic conductivities

Given:

$\lambda_+^\circ = 57\ \mathrm{S\,cm^2\,mol^{-1}}$ $\lambda_-^\circ = 73\ \mathrm{S\,cm^2\,mol^{-1}}$

Hence,

$\Lambda_m^\circ = 57 + 73 = 130\ \mathrm{S\,cm^2\,mol^{-1}}$

4. Match with the options

$130\ \mathrm{S\,cm^2\,mol^{-1}}$

So the correct option is D.