The correct answer is $\boxed{\text{C}}$.
The pH of water is a measure of its acidity or alkalinity. A pH of 7 is neutral, a pH below 7 is acidic, and a pH above 7 is alkaline.
When 0.01 mole of NaOH is added to 10 liters of water, the pH of the water will increase by 1 unit. This is because NaOH is a base, and bases increase the pH of water.
The reason for this is that NaOH dissociates in water to form Na+ and OH- ions. The Na+ ions do not affect the pH of the water, but the OH- ions do. OH- ions are basic, and they react with H+ ions in the water to form H2O. This reaction removes H+ ions from the water, which makes the water more alkaline.
The amount of NaOH that is added to the water is very small, so the change in pH will be small. However, the change in pH will be noticeable, and the water will become slightly more alkaline.
The other options are incorrect because they do not represent the correct change in pH. Option A is incorrect because it states that the pH of the water will decrease by 3 units. This is not possible, because the pH of water cannot be less than 0. Option B is incorrect because it states that the pH of the water will decrease by 4 units. This is also not possible, because the pH of water cannot be less than 0. Option D is incorrect because it states that the pH of the water will not change. This is not possible, because the addition of NaOH will cause the pH of the water to increase.