The geometry of ${\mathrm{H}}_3{\mathrm{O}}^{+}$ ion is

The shape of ${\mathrm{H}}_3{\mathrm{O}}^{+}$is pyramidal as the '3' hydrogen atoms lie at three corners of oxygen as a triangle, and one lone pair of electrons on oxygen attains a pyramidal shape. Due to the repulsion between lone pair and bond pair, the shape is pyramidal.