The nature of the aqueous solution of CsO₂ is ______________.

Aqueous solution of CsO₂ is basic in nature.
If we make an aqueous solution of CsO₂ we get CsOH, O₂ and H₂O₂  as the end products of the reaction. Here CsOH is basic in nature as metal hydroxides are always basic in nature. So, the whole solution will become basic in nature.
CsO₂(s) $+$ H₂O(l) $\to$ CsOH(aq) $+$ O₂(g) $+$ H₂O₂(aq)