What is the best description of the change that occurs when $Na_2O(s)$ is dissolved in water?

Question

$\begin{array}{1 1} \text{(a) Oxidation number of oxygen increases} \\ \text{ (b) Oxidation number of sodium decreases} \\ \text{ (c) Oxide ion accepts sharing in a pair of electrons} \\ \text{ (d) Oxide ion donates a pair of electrons} \end{array}$