Introduction:
The gas used to inflate the tires of an aircraft is nitrogen. Nitrogen is the preferred gas for tire inflation in aircraft due to its unique characteristics and benefits. In this response, we will explain why nitrogen is chosen over other gases like hydrogen, helium, and neon for aircraft tire inflation.

Benefits of Nitrogen:
There are several reasons why nitrogen is the preferred gas for inflating aircraft tires:

1. Chemical Stability: Nitrogen is an inert gas, which means it does not react with other substances easily. This chemical stability reduces the risk of corrosion and oxidation inside the tire, extending its lifespan.

2. Reduced Fire Hazard: Nitrogen is non-flammable, unlike hydrogen and helium, which are highly flammable gases. This makes nitrogen a safer choice in case of a tire-related fire incident.

3. Less Pressure Variation: Nitrogen has a lower rate of pressure variation with temperature changes compared to other gases. This is important for maintaining tire pressure within the desired range, as temperature fluctuations occur during flight.

4. Improved Tire Performance: Nitrogen-filled tires provide better stability and handling characteristics compared to tires filled with compressed air. This is particularly crucial in aviation, where precise control and maneuverability are essential.

5. Prevention of Moisture Build-up: Nitrogen is a dry gas, meaning it does not contain moisture. Moisture inside the tire can lead to corrosion, rust, and degradation of the tire structure. Nitrogen inflation helps prevent moisture build-up and maintains tire integrity.

Comparison with Other Gases:
Let's briefly compare nitrogen with the other gases mentioned in the question:

- Hydrogen: Hydrogen is highly flammable and poses a significant fire hazard. It is not suitable for tire inflation in aircraft due to safety concerns.

- Helium: Helium is also a flammable gas, although less so than hydrogen. However, its use in aircraft tire inflation is limited because it is a relatively expensive gas compared to nitrogen.

- Neon: Neon is an inefficient gas for tire inflation as it has a lower molecular weight than nitrogen. This means it can leak more easily through the tire's rubber structure, leading to faster pressure loss.

Conclusion:
In conclusion, the gas used to inflate the tires of an aircraft is nitrogen. Nitrogen provides several benefits such as chemical stability, reduced fire hazard, less pressure variation, improved tire performance, and prevention of moisture build-up. It is the preferred choice due to its safety, reliability, and compatibility with the unique requirements of aircraft tire inflation.