1. Bronchid’s concept of acid & base:-

According to Bronchid’s concept, an acid a is a substance which can donate proton H⁺, while a base is a substance which can accept proton H⁺ ion hence an acid is a proton-doner, & base is a proton acceptor.

For Example

HCl & Cl^- Conjugate- acid – base pair

NH₃ & NH₄⁺ are conjugate acid base pair.

Hence, the pair of acid & base which are formed from each other by the gain or loss of a proton are could conjugate acid-base pair.

Acid = Conjugate base + H⁺

Base = Conjugate acid – H⁺

Limitation of Bronchid’s Concepts:-

1. Like Arrhenius concepts, it doesn’t explain the acidic basic nature of oxide like CO₂, SO₂ etc.
2. Substances like BF₃ or AlCl₃ act as acid but not proton donor.