Answer:
See Explanation
Step-by-step explanation:
Let us consider the ionization of these compounds;
H3PO4 ⇔3H^+ + PO4^3-
H3BO3 ⇔3H^+ + BO3^3-
The next to consider is the type of electrolyte the both solution are; the both solutions are weak electrolytes and weak electrolytes do not ionize to a large extent.
The implication of this is that, not so much number of ions is added to the solution due to the poor ionization of these weak electrolytes. Hence, in spite of the subscript of 3, the conductivity of the solution does not significantly improve for the reason stated here quite unlike when strong electrolytes are used.