Acid : H₂CO₃
Base : OH⁻
Conjugate Base(CB) : CO₃²
Conjugate Acid(CA) : H₂O
Further explanation
According to Bronstead-Lowry
Acid = proton donor (H +)
Base = proton acceptor (H +)
The conjugate base is the acid that has given the proton
A conjugate acid is a base that has accepted a proton
The conjugate acid ⇄ base + H +
Base + H + ⇄ Conjugate acid
Bronstead-Lowry reaction for acid-base :
HA(acid) + B⁻(base) ⇒ A⁻(CB) + HB(CA)
Reaction
H₂CO₃ + NaOH ⇒ Na₂CO₃ + H₂O
H₂CO₃(acid) + OH⁻(base) ⇒ CO₃²⁻(CB) + H₂O(CA)