Answer
Sodium sulfate is the limiting reactant.
$8.6\ g\ Na_2S$
Work Step by Step
Number of moles of the reactants:
Sulfate: $15\ g\div 142.04\ g/mol=0.11\ mol$
Carbon: $7.5\ g\div12.011\ g/mol=0.62\ mol$
Ratio: $0.62/0.11=5.9$
Sodium sulfate is the limiting reactant.
From stoichiometry:
$0.11\ mol\times 1_{Na_2S}/1_{Na_2SO_4} \times 78.04\ g/mol\ Na_2S=8.6\ g\ Na_2S$
