What is the concentration of NaNO2 if 2.13g of N2O3 is added to excess NaOH and the resulting solution is diluted to a total volume of 500.0 mL?

Answer 1

Do you want concn in units of molar? molality? normality, grams/L, or just what. The easy way to answer is g/L.
2.13 g is dissolved in 500 mL so the concn is 4.26 g/L.
or 2.13/500 = ??g/mL.
Or 2.13/molar mass = moles and
M = moles/L = ??