* Understanding Reactivity: Reactivity with oxygen is determined by how easily an element loses electrons (its tendency to be oxidized). This is generally related to the element's position on the periodic table.

* Periodic Trends: Elements on the left side of the periodic table tend to lose electrons easily, while those on the right side tend to gain electrons. Elements further down a group (column) are also more reactive.

Let's look at your list:

* Fe (Iron): Iron is a transition metal and is moderately reactive with oxygen. It forms rust (iron oxide) in the presence of air and moisture.

* Si (Silicon): Silicon is a metalloid and is less reactive than iron. It forms a protective oxide layer that slows down further reactions.

* C (Carbon): Carbon is a nonmetal and is relatively unreactive at room temperature. It burns in the presence of oxygen to form carbon dioxide.

* S (Sulfur): Sulfur is a nonmetal and is more reactive than carbon. It burns readily in oxygen to form sulfur dioxide.

* P (Phosphorus): Phosphorus is a nonmetal and is highly reactive with oxygen. It reacts spontaneously with oxygen to form phosphorus oxides (P4O6 or P4O10).

Conclusion:

Based on their positions in the periodic table and their known reactivity, the elements listed in order of increasing reactivity with oxygen are:

1. C (Carbon)

2. Si (Silicon)

3. Fe (Iron)

4. S (Sulfur)

5. P (Phosphorus)

Therefore, Phosphorus (P) reacts the fastest with oxygen.