The species: can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and base.

Bronsted acid: A bronsted acid is a substance that can donate a proton. A bronsted acid is proton-donor.

Bronsted base: A bronsted base is a substance that can accept a proton from an acid. A bronsted base is proton-acceptor.

When a base gain a proton, the residual part of it has a tendency to accept the proton. Therefore, it behaves as conjugate acid.

When an acid loses a proton, the residual part of it has a tendency to regain a proton. Therefore, it behaves as a conjugate base.

Conjugate base ⇌ Conjugate acid - H⁺

Conjugate base ⇌ Conjugate acid + H⁺