The reactant concentration in a zero-order reaction was 5.00×10⁻² M after 190 s and 2.00×10⁻² M after 400 s. What is the rate constant for this reaction? Express your answer with the appropriate units. Indicate the multiplication of units, as necessary, explicitly either with a multiplication dot or a dash.

A) 1.25×10⁻⁴ M/s
B) 1.25×10⁻⁴ mol/Ls
C) 7.50×10⁻⁵ mol/Ls
D) 7.50×10⁻⁵ M/s