## **Core Concept**
The question tests understanding of enzyme kinetics, specifically types of enzyme inhibition. **Enzyme inhibition** is a process where the activity of an enzyme is reduced by a molecule called an inhibitor. There are several types of inhibition, including competitive, non-competitive, uncompetitive, and mixed inhibition, each affecting **Vmax** (maximum velocity) and **Km** (Michaelis constant) differently.

## **Why the Correct Answer is Right**
The correct answer, **competitive inhibition**, is characterized by an increase in **Km** (the substrate concentration at which the reaction rate is half of Vmax) but no change in **Vmax**. This type of inhibition occurs when the inhibitor structurally resembles the substrate and competes with it for binding to the **active site** of the enzyme. As a result, more substrate is needed to achieve half the maximum velocity (increased Km), but if enough substrate is added, the inhibitor can be completely outcompeted, and the enzyme can reach its original maximum velocity (Vmax remains the same).

## **Why Each Wrong Option is Incorrect**
- **Option A (Non-competitive inhibition):** In non-competitive inhibition, **Vmax decreases**, but **Km remains unchanged**. The inhibitor binds to an allosteric site on the enzyme, changing its shape and affecting its ability to convert substrate to product, regardless of the substrate concentration.
- **Option C (Uncompetitive inhibition):** Uncompetitive inhibition is characterized by a **decrease in both Km and Vmax**. The inhibitor binds to the enzyme-substrate complex, reducing both the maximum velocity and the affinity of the enzyme for the substrate.
- **Option D (Mixed inhibition):** Mixed inhibition involves a combination of competitive and non-competitive inhibition, where **both Km and Vmax change**. The inhibitor can bind to both the free enzyme and the enzyme-substrate complex, altering both the affinity of the enzyme for the substrate (Km) and the maximum velocity (Vmax) of the reaction.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in **competitive inhibition**, the effect can be overcome by increasing the substrate concentration, which is a strategy used in some clinical scenarios. For example, in methanol or ethylene glycol poisoning, fomepizole (an alcohol dehydrogenase inhibitor) competitively inhibits alcohol dehydrogenase; however, the treatment involves supportive care and sometimes hemodialysis, not merely increasing substrate.

## **Correct Answer:** . **Competitive inhibition**