The conjugate base of hydrazoic acid is:

Hydrazoic acid is a chemical compound with the formula HN₃. It is an acid, meaning it can donate a proton (H⁺ ion). The conjugate base of an acid is formed when the acid loses one proton (H⁺).

For hydrazoic acid (HN₃), the dissociation reaction can be written as:

$$ \text{HN}_3 \rightarrow \text{H}^+ + \text{N}_3^- $$

When HN₃ loses a proton (H⁺), the remaining species is N₃⁻. Therefore, the conjugate base of hydrazoic acid is N₃⁻.

Now, let's examine the options:

Option A: N⁻³ (written as N$$^{-3}$$) represents the nitride ion, which is not related to hydrazoic acid. The nitride ion is the conjugate base of ammonia (NH₃) after losing three protons, but hydrazoic acid loses only one proton.

Option B: N$$_3^-$$ represents N₃⁻, which matches the conjugate base we derived from HN₃.

Option C: N$$_2^-$$ represents N₂⁻, which is not the conjugate base of hydrazoic acid. Hydrazoic acid has three nitrogen atoms, so losing a proton should leave N₃⁻, not N₂⁻.

Option D: HN$$_3^-$$ represents HN₃⁻, which implies the acid molecule with an extra electron. This is incorrect because the conjugate base is formed by losing a proton (H⁺), not gaining an electron.

Therefore, the conjugate base of hydrazoic acid is N₃⁻, which corresponds to Option B.

Hence, the correct answer is Option B.