The decomposition of ozone is believed to occur by mechanism :
`O_3 rightarrow O_2+O`(fast)
` O+O_3 rightarrow 2O_2`
When the concentration of `O_(2)` is increased. The rate of decomposition of ozone ……. .

Options

A. increases
B. decreases
C. remains the same
D. cannot be answered

Explanation

To solve the question regarding the decomposition of ozone and the effect of increased oxygen concentration on the rate of decomposition, we can follow these steps:

### Step 1: Understand the Reaction Mechanism
The decomposition of ozone (\(O_3\)) occurs via the following steps:
1. \(O_3 \rightarrow O_2 + O\) (fast step)
2. \(O + O_3 \rightarrow 2O_2\) (slow step)

### Step 2: Identify the Rate-Determining Step
The slow step in the mechanism is the rate-determining step. This means that the rate of the overall reaction is dependent on this step. In this case, the slow step is:
\[ O + O_3 \rightarrow 2O_2 \]

### Step 3: Write the Rate Law for the Rate-Determining Step
The rate law for the slow step can be expressed as:
\[ \text{Rate} = k [O][O_3] \]
where \(k\) is the rate constant, \([O]\) is the concentration of atomic oxygen, and \([O_3]\) is the concentration of ozone.

### Step 4: Consider the Effect of Increased Oxygen Concentration
When the concentration of molecular oxygen (\(O_2\)) is increased, we need to analyze how this affects the concentration of atomic oxygen (\(O\)). From the fast step, we can deduce that:
\[ [O] \text{ is produced from } O_3 \text{ and is consumed in the slow step.} \]

### Step 5: Analyze the Impact on the Rate
If the concentration of \(O_2\) increases, it indicates that the concentration of atomic oxygen (\(O\)) may decrease due to the equilibrium established in the fast step. Since the rate of the slow step depends on the concentration of \(O\), an increase in \(O_2\) leads to a decrease in \(O\), which in turn decreases the rate of decomposition of ozone.

### Conclusion
Therefore, when the concentration of \(O_2\) is increased, the rate of decomposition of ozone decreases.

### Summary of Steps:
1. Understand the reaction mechanism.
2. Identify the rate-determining step.
3. Write the rate law for the slow step.
4. Consider the effect of increased \(O_2\) concentration.
5. Analyze the impact on the rate of decomposition.