Question

Which gas in the air is essential for burning wood?
A. Nitrogen
B. Hydrogen
C. Oxygen
D. Helium

Answer 1

Hint: Burning of wood is the process of combustion. Combustion refers to the process where a substance burns in the presence of oxygen, giving off heat and light in the process.

Complete solution:
Many materials in our environment, including wood, burn indirectly in the sense that the material does not burn, it’s a combustion process that takes place as a reaction between oxygen and the gases released from a material. Under this influence of heat, wood produces substances that react eagerly with oxygen, leading to the high propensity of wood to ignite and burn.

We know burning of wood is actually several processes. We will try to break it down as simply as possible, though the detailed chemistry is incredibly complex.
The first process is pyrolysis. During pyrolysis heat from the flames cause the wood to decompose into char (carbon) and volatile organic compounds, or VOCs. The burning of the VOCs provides most of the flames you see.
As char starts to form it too begins to react with oxygen in a second process known as gasification. During gasification oxygen, and to a lesser extent carbon dioxide (\[C{O_2}\]) and water (${H_2}O$) diffuse into pores in the char and react with the char carbon to produce carbon monoxide ($CO$). Any residual organic matter is likewise oxidized to produce CO and${H_2}O$.
Once in the gas phase, $CO$, in the presence of ${H_2}O$ can react with oxygen to form \[C{O_2}\]. If you look closely at burning logs after the wood has been thoroughly pyrolyzed to char you might see a faint glow around the surface of the char, only a few mm thick. That glow is the result of chemiluminescence, which happens when certain compounds are oxidized in the gas phase.
So we have learned the process of burning wood and we come to know that oxygen is the most essential gas for burning wood.

Correct option: C. Oxygen

Note:
We can ask similar types of questions if we have basic knowledge of combustion and other gases which are given in option. We can use option elimination methods to tackle these type of questions.