A student investigated the stoichiometry of the precipitation reaction between an unknown metal cation, \(\text{M}^{x+}\text{(aq)}\), and phosphate ions, \(\text{PO}_4^{3-}\text{(aq)}\). To five separate beakers, each containing exactly \(30.0\text{ mL}\) of \(0.20\text{ M M(NO}_3\text{)}_x\text{(aq)}\), the student added different volumes of \(0.20\text{ M Na}_3\text{PO}_4\text{(aq)}\). After mixing thoroughly, the precipitate formed in each beaker was collected by filtration, dried, and weighed. The amount of precipitate collected in each beaker is plotted in the graph below.

Based on the graph, which of the following is the empirical formula of the precipitate, and which species is the limiting reactant when \(30.0\text{ mL}\) of \(0.20\text{ M Na}_3\text{PO}_4\text{(aq)}\) is added?