Which of the following is correct about the adsorption of `N_(2)` over lron ?

Options

A. It is always physically adsorbed
B. Extent of adsorption over iron decreases with the increase in temperature first and then increases
C. It is always chemically adsorbed
D. `N_(2)` is never adsorbed over iron

Answer

To determine the correct statement about the adsorption of \(N_2\) over iron, we need to analyze the nature of adsorption and the factors influencing it.

### Step-by-Step Solution:

1. **Understanding Adsorption**: Adsorption is the process where molecules adhere to a surface. There are two main types of adsorption: physical (physisorption) and chemical (chemisorption).

2. **Physical Adsorption**: This type of adsorption occurs due to weak van der Waals forces. It is generally favored at low temperatures because the weak interactions can be maintained without the added energy that higher temperatures provide.

3. **Chemical Adsorption**: This involves the formation of stronger chemical bonds between the adsorbate (in this case, \(N_2\)) and the adsorbent (iron). This process requires a higher activation energy and is favored at higher temperatures.

4. **Temperature Effects**: At low temperatures, \(N_2\) is likely to be physically adsorbed onto iron due to the weak forces involved. As the temperature increases, the kinetic energy of the molecules also increases, which can lead to the breaking of these weak bonds.

5. **Extent of Adsorption**: The extent of adsorption typically decreases with an increase in temperature for physical adsorption. However, once a certain temperature threshold is reached, chemical adsorption may begin to occur, leading to an increase in the extent of adsorption again.

6. **Conclusion**: Therefore, the correct statement regarding the adsorption of \(N_2\) over iron is that it is always physically adsorbed at low temperatures, and the extent of adsorption decreases with increasing temperature until it potentially transitions to chemical adsorption.

### Final Answer:
The correct statement is that \(N_2\) is always physically adsorbed over iron at low temperatures.