Final answer:
A substance that can accept or donate protons in reaction to changes in H+ concentration is known as a Brönsted-Lowry base, which can also be amphiprotic like water.
Step-by-step explanation:
A substance that accepts H+ ions (protons) when they are in excess and donates H+ when their concentration drops is called a Brönsted-Lowry base. These substances can act as proton acceptors in a chemical reaction, and some, like water, are also capable of donating a proton, depending on the circumstances, which makes them amphiprotic. Examples of bases in this context include bicarbonate (HCO3−) and ammonia (NH3).