At low pressure, the fraction of the surface covered follows.

Options

A. zero-order kinetics
B. first order kinetics
C. second order kinetics
D. fractional order kinetics

Explanation

To solve the question regarding the fraction of the surface covered at low pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept**: At low pressures, the fraction of the surface covered by the adsorbate can be described by an equation that relates the amount adsorbed to the pressure of the gas.

2. **Equation Formulation**: The relationship can be expressed as:
\[ \frac{x}{m} = k \cdot p^{\frac{1}{n}} \]
where:
- \( \frac{x}{m} \) is the fraction of the surface covered,
- \( p \) is the pressure,
- \( k \) is a constant,
- \( n \) is a parameter that can vary depending on the system.

3. **Identifying Proportionality**: At low pressures, we can simplify our understanding of the equation. If we assume that \( n = 1 \), the equation simplifies to:
\[ \frac{x}{m} \propto p \]
This indicates that the fraction of the surface covered is directly proportional to the pressure.

4. **Kinetics Order**: Since the relationship shows that the fraction of surface coverage increases linearly with pressure, we can conclude that this behavior follows first-order kinetics. In first-order kinetics, the rate of reaction is directly proportional to the concentration of one reactant.

5. **Conclusion**: Thus, at low pressure, the fraction of the surface covered follows first-order kinetics.

### Final Answer:
The fraction of the surface covered at low pressure follows first-order kinetics.

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