Decomposition of `NH_(3)` on the surface of tungsten is a reaction of :

Options

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

Explanation

To determine the order of the reaction for the decomposition of ammonia (NH₃) on the surface of tungsten, we need to analyze the characteristics of the reaction.

### Step-by-Step Solution:

1. **Identify the Reaction**: The decomposition of ammonia (NH₃) on the surface of tungsten can be represented as:
\[ 2NH_3(g) \rightarrow N_2(g) + 3H_2(g) \]
This reaction involves gaseous reactants and products.

2. **Identify the Catalyst**: Tungsten (W) acts as a catalyst in this reaction. A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.

3. **Determine the Type of Catalyst**: Since tungsten is a solid and the reactants and products are gases, this reaction is classified as a **heterogeneous catalytic reaction**. In heterogeneous reactions, the catalyst is in a different phase than the reactants.

4. **Consider the Order of Reaction**: In heterogeneous catalysis, the reaction rate often depends on the surface area of the catalyst and the concentration of the gaseous reactants. However, when the reaction is limited by the surface area of the catalyst, it can exhibit zero-order kinetics.

5. **Conclusion**: Therefore, the decomposition of ammonia on the surface of tungsten is a **zero-order reaction** with respect to ammonia. This means that the rate of reaction is constant and does not depend on the concentration of ammonia.

### Final Answer:
The decomposition of NH₃ on the surface of tungsten is a reaction of **zero order**.