**Core Concept**
The pH of a solution is a measure of its acidity or alkalinity, defined as the negative logarithm of the concentration of hydrogen ions (H+) in moles per liter (mol/L). The pH scale ranges from 0 to 14, with a pH of 7 being neutral, below 7 acidic, and above 7 alkaline.

**Why the Correct Answer is Right**
To determine the pH of the solution, we use the formula pH = -log[H+], where [H+] is the concentration of hydrogen ions in moles per liter. Given that the concentration of hydrogen ions is 1 x 10-7 moles/liter, we can plug this value into the formula to calculate the pH. By taking the negative logarithm of 1 x 10-7, we get a pH of 7, indicating a neutral solution.

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no calculation provided to support this answer, and it does not take into account the correct formula for calculating pH.
* **Option B:** This option is incorrect because the pH of a solution cannot be negative, as the pH scale ranges from 0 to 14.
* **Option D:** This option is incorrect because it does not accurately reflect the calculation for pH, and the value provided is not consistent with the given concentration of hydrogen ions.

**Clinical Pearl / High-Yield Fact**
Remember the pH formula: pH = -log[H+]. This simple formula allows you to quickly determine the acidity or alkalinity of a solution based on the concentration of hydrogen ions.

**Correct Answer:** C. 7