* The pH scale: The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 to 14, with:

* 0 to 6.9: Acidic

* 7: Neutral

* 7.1 to 14: Alkaline (basic)

* Water's autoionization: Pure water undergoes a process called autoionization, where a small fraction of water molecules spontaneously ionize into hydrogen ions (H+) and hydroxide ions (OH-):

```

H2O ⇌ H+ + OH-

```

* Equal concentrations: In pure water, the concentration of H+ ions is equal to the concentration of OH- ions. This is why pure water is considered neutral.

* The pH equation: The pH of a solution is calculated using the following equation:

```

pH = -log[H+]

```

Where [H+] represents the concentration of hydrogen ions.

* Neutral pH = 7: Since the concentrations of H+ and OH- are equal in pure water, the log of their concentration is zero. Therefore, the pH of pure water is -log(1) = 7.

In summary: Pure water is neutral because the concentrations of H+ and OH- ions are equal. This balance results in a pH of 7 on the pH scale.