**Core Concept**
The question is testing the understanding of enzyme kinetics and the effect of inhibitors on enzyme activity. Km (Michaelis constant) is a measure of the affinity of an enzyme for its substrate, while Vmax (maximal velocity) is a measure of the maximum rate of enzyme catalysis. Changes in Km or Vmax can provide insight into the mechanism of enzyme inhibition.

**Why the Correct Answer is Right**
An increase in Km indicates that the enzyme is less efficient at binding to its substrate, while maintaining the same Vmax suggests that the enzyme is not being inhibited from catalyzing the reaction. This is characteristic of non-competitive inhibition, where the inhibitor binds to a site other than the substrate-binding site, reducing the enzyme's affinity for the substrate without affecting its catalytic activity.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because competitive inhibition would decrease Vmax, not leave it unchanged.
**Option B:** This is incorrect because non-competitive inhibition would decrease Vmax, not leave it unchanged.
**Option C:** This is incorrect because uncompetitive inhibition would decrease both Km and Vmax.

**Clinical Pearl / High-Yield Fact**
In non-competitive inhibition, the inhibitor binds to a site on the enzyme that is not involved in substrate binding, effectively reducing the enzyme's affinity for the substrate without affecting its catalytic activity. This type of inhibition is often seen with irreversible inhibitors that covalently modify the enzyme.

**Correct Answer: C. Non-competitive inhibition.**