Sodium oxide reacts with water to produce sodium hydroxide. 20.0 g of sodium oxide is dissolved in 500 mL of water. Neglecting the change in volume, the concentration of the resulting NaOH solution is ______________ $\times$ 10^$-$1 M. (Nearest integer) [Atomic mass : Na = 23.0, O = 16.0, H = 1.0]