What happens in a bronsted-lowry acid-base reaction?

A. An acid donates an H⁺, and a base accepts an H⁺.

Explanation:

According to Bronsted-Lowry Model :

The letter A is the right answer.

Explanation:

Danish Johannes Nicolaus Brönsted (1879-1947) and Englishman Thomas Martin Lowry (1874-1936) proposed an acid-base theory known as the Brönsted-Lowry theory, which reads as follows:

Acid is a chemical substance that necessarily donates H⁺ protons, while a Base is a chemical substance that necessarily receives H⁺ protons.

In this case, the proton is considered the hydrogen ion. This is seen in the following reaction, where hydrocyanic acid donates a proton to water, which acts as a base:

HCN + H2O → CN- + H3O⁺  

This reaction is reversible, and the hydronium ion (H3O +) can donate a proton to the CN- ion. Thus, hydronium ion (H3O +) acts as acid and CN- as base.

CN- + H3O⁺→ HCN + H2O