What is the molarity of a solution prepared by dissolving 12.0 g of sodium acetate, nac2h3o2, in water and diluting it to 250.0 ml?

Molarity is defined as the number of moles of solute in 1 L of solution 
the mass of sodium acetate added - 12.0 g 
molar mass of sodium acetate - 82 g/mol
number of moles = mass present / molar mass
number of moles of sodium acetate added = 12.0 g / 82 g/mol = 0.146 mol
the number of moles in 250.0 mL - 0.146 mol
therefore number of moles in 1000 mL - 0.146 mol / 250.0 mL x 1000 mL/L = 0.584 mol
there are 0.584 mol in 1 L - 0.584 mol/L
the molarity of sodium acetate is 0.584 M

Mgo2 is the oxidation state of manganese oxide