The reaction between iron metal and oxygen gas to form solid oxide is a combustion reaction, specifically the formation of iron oxide (rust). Here's the balanced chemical equation:

4 Fe (s) + 3 O₂ (g) → 2 Fe₂O₃ (s)

Explanation:

* Fe (s): Iron in its solid metallic form.

* O₂ (g): Oxygen gas.

* Fe₂O₃ (s): Iron(III) oxide, commonly known as rust, in solid form.

Process:

1. Iron reacts with oxygen in the presence of moisture (water).

2. The oxygen atoms combine with iron atoms, forming iron oxide.

3. This reaction is exothermic, meaning it releases heat.

4. The process is often slow, but it can be accelerated by factors like humidity, salt, and acids.

Note:

* There are multiple forms of iron oxide, but the most common product of this reaction is iron(III) oxide (Fe₂O₃).

* The presence of moisture is crucial for this reaction to occur, as it acts as an electrolyte to facilitate the transfer of electrons.

* The rusting of iron is a significant concern in many industries, as it can weaken structures and cause corrosion.