Which of the following statements is not true ?

Options

A. Ammonia acts as sink fo `NO_(x)`
B. Limestone acts as sink for `SO_(x)`
C. The average residence time of NO is one month
D. `SO_(x)` can be removed from flue gases by passing through a solution of citrate ions

Explanation

To determine which statement is not true, let's analyze each option provided in the question:

1. **Ammonia acts as a sink for NOx**:
- This statement is true. Ammonia (NH3) can react with nitrogen oxides (NOx) to form ammonium salts, effectively removing NOx from the atmosphere.

2. **Limestone acts as a sink for SOx**:
- This statement is also true. Limestone (calcium carbonate, CaCO3) can react with sulfur oxides (SOx) to form calcium sulfate, which helps in reducing SOx emissions.

3. **The average residence time of NO is 1 month**:
- This statement is not true. The average residence time of nitric oxide (NO) in the atmosphere is typically around 0.5 to 2 days, not 1 month.

4. **SOx can be removed from flue gas by passing through a solution of citrate ions**:
- This statement is true. Citrate ions can react with sulfur oxides in flue gas, helping to remove them from emissions.

Based on the analysis, the statement that is not true is:

**The average residence time of NO is 1 month.**

### Step-by-Step Solution:
1. **Identify the statements provided in the options.**
2. **Evaluate each statement for its truthfulness.**
3. **Determine the average residence time of NO based on known data.**
4. **Identify the statement that does not align with factual information.**