**Why Oxygen is Necessary for Combustion**

Combustion is a chemical reaction that occurs between a fuel source and an oxidizing agent, typically oxygen. Oxygen plays a crucial role in combustion reactions as it acts as the primary oxidizer. The process of combustion involves the rapid combination of fuel with oxygen, releasing energy in the form of heat and light.

**Oxygen as an Oxidizing Agent**

1. **Oxidation-Reduction Reactions:** Combustion is essentially an oxidation-reduction (redox) reaction, where the fuel undergoes oxidation and the oxidizing agent, in this case oxygen, undergoes reduction. Oxygen is a highly electronegative element, meaning it has a strong tendency to attract electrons. During combustion, oxygen accepts electrons from the fuel, causing it to become reduced.

2. **Energy Release:** The energy released during combustion results from the transfer of electrons from the fuel to oxygen. This transfer of electrons is what allows the fuel molecules to break apart and recombine with oxygen, forming new compounds and releasing heat and light energy. Without oxygen, the combustion process would not occur, and the fuel would remain stable.

**Oxygen's Role in the Combustion Process**

1. **Activation Energy:** Combustion reactions require an initial input of energy, known as activation energy, to start the reaction. Oxygen plays a vital role in providing this activation energy by readily reacting with the fuel. The reaction between oxygen and the fuel molecules initiates the release of energy, allowing the combustion process to proceed.

2. **Chain Reaction:** Once the combustion reaction begins, it often becomes self-sustaining due to a chain reaction. In this process, the initial reaction between the fuel and oxygen produces heat, which then provides the activation energy required for the subsequent fuel molecules to react with oxygen. Oxygen molecules continuously react with fuel until the fuel source is exhausted or the reaction is controlled.

**Other Factors Influencing Combustion**

1. **Stoichiometric Ratio:** The stoichiometric ratio refers to the ideal ratio of fuel to oxygen required for complete combustion. In most cases, a specific amount of oxygen is needed to ensure the combustion process proceeds efficiently. If the oxygen supply is limited, incomplete combustion may occur, leading to the formation of harmful byproducts such as carbon monoxide.

2. **Temperature and Pressure:** The availability of oxygen also depends on the surrounding temperature and pressure. Higher temperatures and increased pressure can promote more efficient combustion by increasing the collision rate between fuel and oxygen molecules.

In summary, oxygen is necessary for combustion due to its role as the primary oxidizing agent. It provides the activation energy required to initiate the combustion reaction and allows for the transfer of electrons from the fuel, resulting in the release of energy. Without oxygen, the combustion process cannot occur, and the fuel would remain unreactive.

Oxygen is a supporter of combustion...whereas the other gases are either non-supporter of combustion or they are combustible...for e.g. hydrogen is combustible and burns with a pop sound whereas carbon dioxide is neither combustible nor it supports combustion...thus oxygen is the one and only gas which is essential for combustion...