Elements of group-15 form compounds in +5 oxidation state. However, bismuth forms only one well-characterized compound in +5 oxidation state. The compound is-

Hint: Element shows its higher oxidation state with electronegative element only

Stability of + 5 oxidation state decreases top to bottom and + 3 oxidation state increases top to bottom due to inert pair effect. Meanwhile compound having + 5 oxidation state of $\mathrm{Bi}$ is ${\mathrm{BiF}}_{5}$. It is due to smaller size and high electronegativity of fluorine.