Final answer:
The element that forms the fluorides XF₃ and XF₅, and reacts with sodium to form Na₃X is antimony (Sb). Antimony can exhibit both +3 and +5 oxidation states, aligning with the described chemical behavior.
Step-by-step explanation:
The student has asked about an element, X, that forms the fluorides XF₃ and XF₅, and also reacts with sodium to form Na₃X. Given this information, the element X must have the capability to form both +3 and +5 oxidation states, and also be able to form an ionic compound with sodium where it has a -3 charge.
One such element that has these properties is antimony (Sb). Antimony can form the trihalide SbF₃ and the pentahalide SbF₅. It also reacts with sodium to form Na₃Sb, consistent with the properties described for element X. This behavior is typical of elements within Group 15 of the periodic table, where multiple oxidation states are possible.
Examples:
- 2NaF(s) + SbF₃(g) → Na₃SbF₆(s)
- Sb + 3F₂(g) → SbF₆(s)
- 3Na + Sb → Na₃Sb