To identify the isostructural pairs among the given species, we first need to understand their molecular geometries and the electron-pair arrangements.

1. NF₃: Nitrogen trifluoride has a trigonal pyramidal structure due to the presence of one lone pair of electrons on nitrogen. It follows the AX₃E steric number formula (where A is the central atom, X represents bonded atoms, and E represents lone pairs).

2. $$NO_3^-$$: The nitrate ion has a trigonal planar structure. This can be rationalized using VSEPR theory, where it follows the AX₃ steric number formula with no lone pairs on the central nitrogen atom.

3. BF₃: Boron trifluoride is also trigonal planar. It conforms to the AX₃ steric number formula with no lone pairs on boron.

4. H₃O⁺: The hydronium ion has a trigonal pyramidal structure, similar to NF₃, with one lone pair of electrons. It follows the AX₃E formula.

5. HN₃: Hydronitrenium ion has a linear or slightly bent structure, depending on how we look at the resonance structures. Overall, it does not share the same geometric configuration with any of the molecules listed above.

From the above analysis:

• Isostructural Pair 1: NF₃ and H₃O⁺ (both have a trigonal pyramidal structure)
• Isostructural Pair 2: $$NO_3^-$$ and BF₃ (both have a trigonal planar structure)

Therefore, the correct option is:

Option C:

[NF₃, H₃O⁺] and [$$NO_3^-$$, BF₃].