In which of the following will the corrosion of iron be most rapid?

Options

A. In pure water
B. In pure oxygen
C. In air and moisture
D. In air and saline water

Explanation

To determine in which environment the corrosion of iron will be most rapid, we need to analyze the options provided:

1. **In pure water**:
- Iron can corrode in pure water, but the process is relatively slow. A protective oxide layer can form, which slows down further corrosion.

2. **In pure oxygen**:
- While oxygen is necessary for corrosion, pure oxygen alone does not provide the moisture needed for rapid corrosion. Therefore, corrosion would not be very rapid in this environment.

3. **In air and moisture**:
- The presence of moisture in the air can lead to corrosion, as iron reacts with water and oxygen to form rust (iron oxide). However, the protective oxide layer can still form, which may slow down the process.

4. **In air and saline water**:
- Saline water contains salt, which enhances the electrochemical reactions that lead to corrosion. The presence of salt prevents the formation of a protective oxide layer, allowing the corrosion process to continue rapidly.

Based on this analysis, the environment in which the corrosion of iron will be most rapid is:

**Answer**: In air and saline water.