Which of the following can act both as Bronsted acid and Bronsted base
HCO3-
Those substance accept the proton are called Bronsted base and which is
donate the proton are called Bronsted acid.
HCO−3 + H+ ⇌ H2CO3 Bronsted base.
HCO−3 ⇌H+ + CO2−3 Bronsted acid.