The correct option is A 6.5 - 7.5
The strength of acidic and basic substances is measured with respect to pH scale. The standard value of an acid on a pH scale is between 0 - 7, the substances that are basic have the value ranging between 7 - 14 and for neutral substances the pH is around 7. Since pure water is neither an acid nor a base but neutral, the pH range most suitable can be 6.5 to 7.5.