Order Acid strength and Explain how to order : N^3- NH^2- HSO4^- SO4^2-?

Acids and bases....

First of all, there is no such ion as N^3- in aqueous solution. It would be too basic and react with water, producing hydroxide ions.
Li3N(s) + 3HOH(l) --> NH3(aq) + 3LiOH(aq)
(Lithium nitride is the only stable alkali metal nitride.)
We could hypothetically write:
N^3- + HOH <==> NH^2- + OH-
N^3- + 2HOH <==> NH2^- + 2OH-
N^3- + 3HOH <==> NH3 + 3OH-

NH^2- + 2HOH <==> NH3 + 2OH-
N^3- is a stronger base than NH^- or NH2^-

HSO4^- is a weak acid (Ka=1.2x10^-2)
HSO4^- <==> H+ + SO4^2-

SO4^2- is a weak base.
SO4^2- + HOH <==> HSO4^- + OH-

Acid strength ----
least ..................... ...................most
N^3-.... NH^2- ... SO4^2- .... HSO4^-
most basic ........... ........... most acidic

Firstly, consider the basic strengths instead :

N³⁻ + H⁺ ⇌ NH²⁻
NH²⁻ + H⁺ ⇌ NH₂⁻
HSO₄⁻ + H⁺ ⇌ H₂SO₄
SO₄²⁻ + H⁺ ⇌ HSO₄⁻

The stronger the base, the weaker its conjugate acid.
Strength of the conjugate acid : H₂SO₄ > HSO₄⁻ > NH₂⁻ > NH²⁻
Basic strength : HSO₄⁻ < SO₄²⁻ < NH²⁻ < N³⁻

The less basic of a species, the more acidic it is.
Hence, acid strength : HSO₄⁻ > SO₄²⁻ > NH²⁻ > N³⁻