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What defines a neutral solution?

  1. If [H+] is greater than [-OH]

  2. If the concentrations of [H+] and [-OH] are equal

  3. If [H+] is less than [-OH]

  4. If the solution has a pH below 7

The correct answer is: If the concentrations of [H+] and [-OH] are equal

A neutral solution is defined by having equal concentrations of hydrogen ions ([H+]) and hydroxide ions ([OH-]). When the concentrations are balanced in this way, the solution has a pH of exactly 7, which is considered neutral on the pH scale. This balance of ions signifies that the solution is neither acidic nor basic. In a neutral solution, the concentration of [H+] dictates the acidity, while the concentration of [OH-] indicates the basicity. Since acids release [H+] when dissolved in water and bases release [OH-], a neutral solution's state reflects a lack of excess ions from either category. Therefore, the conclusion that the concentrations must be equal to define neutrality is foundational to understanding acid-base chemistry in biological systems. Other options highlight different scenarios, such as indicating conditions where one type of ion predominates over the other or where the pH level suggests acidity, which does not apply to a neutral solution. Thus, the correct identification of a neutral solution is fundamentally rooted in the equality of [H+] and [OH-].