The hybridization of Se in SeF 4 and its geometry respectively are

Selenium has the six unpaired electron in outermost shell for bonding. After that four electrons formed the bonding with the fluorine atoms and one lone pair present on the selenium. It has the see-saw shape geometry because on the repulsion due to lone pair. It has the four bond pair and one lone pair with steric number five. It has the hybridization of ${\mathrm{sp}}^3\mathrm{d}$.

Hence, the hybridization of $\mathrm{Se}$ in ${\mathrm{SeF}}_4$ and its geometry respectively are ${\mathrm{sp}}^3\mathrm{d}$, see-saw shaped.