Final answer:
A solution with a hydrogen ion concentration of 1.00 x 10^-7 M is neutral because its pH is 7, which is the pH of pure water. This represents a balance between hydronium and hydroxide ions, with both being present in equal concentrations.
Step-by-step explanation:
A solution with a hydrogen ion concentration of 1.00 x 10^-7 M is considered neutral because the pH of this solution is 7. pH is calculated by taking the negative logarithm (base 10) of the hydrogen ion concentration. The logarithm of 1 x 10^-7 is -7, and the negative of this is 7, which is the pH of pure water and is defined as a neutral pH.
The balance between hydronium ions (H3O+) and hydroxide ions (OH-) is what characterizes a neutral solution. In pure water at 25 degrees Celsius, the concentrations of H3O+ and OH- are both 1 x 10^-7 M, which is why water is neutral. Additionally, the product of the concentrations of these two ions in any aqueous solution is always 1 x 10^-14.