Acid: Acids are substances that donate protons (H+) in a reaction. They are typically sour in taste and react with metals to produce hydrogen gas. Some common examples of acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3).

Alkali: Alkalis are substances that donate hydroxide ions (OH-) in a reaction. They are typically bitter in taste and feel slippery to the touch. Some common examples of alkalis include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2).

Reaction: When an acid and an alkali react, they undergo a neutralization reaction. In this reaction, the hydrogen ions from the acid and the hydroxide ions from the alkali combine to form water (H2O). The other ions present in the acid and alkali salts form a salt. The general equation for a neutralization reaction is:

```

acid + alkali → salt + water

```

For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the following reaction takes place:

```

HCl + NaOH → NaCl + H2O

```

The products of this reaction are sodium chloride (NaCl) and water (H2O).