Question 25 for each chemical reaction in the table below, decide whether the highlighted reactant is a brønsted-lowry acid, a brønsted-lowry base, or neither.

According to the Bronsted-Lowry definitions, an acid is any substance that donates hydrogen ions; whereas, a base is any substance that accepts hydrogen ions. 

In the first reaction, water is acting as an acid because it donates a hydrogen ions.

In the second reaction, water is acting as a base because it accepts a hydrogen ion.

In the third reaction, water is again donating a hydrogen ion so it is the acid.

In the fourth reaction, water is acting as a base by accepting the hydrogen ion from the ammonium ion.