Definition
A colorless, odorless, tasteless gas that is the lightest of all known elements. Its chemical symbol is H, and it has an atomic number of 1. Hydrogen is highly flammable and, when mixed with air or oxygen in the right proportions, forms an explosive mixture.
Plain English
Hydrogen is the lightest gas there is. You can't see it or smell it, and it burns very easily. Mixed with air, it can explode.
Context Anchor
Seen in lighter-than-air aircraft discussions, fuel and power-system discussions, and safety information about flammable gases.
Derivation
From the Greek hydro (water) and genes (forming) — literally 'water-former,' because burning hydrogen in oxygen produces water. The name reflects what the gas does, not what it looks like, which is why the chemistry of hydrogen is closely tied to water and combustion.
Why Pilots Care
Hydrogen is extremely flammable and requires special handling procedures and storage equipment to prevent fire or explosion risks.
Grounding Statement
If hydrogen leaks, it tends to rise because it is so light, and if it mixes with air near a spark or flame, it can ignite.
Intuition Check
Do not think of hydrogen as safe just because it is very light. In aviation use, its lightness is useful, but its easy ignition is the main safety concern.
Example Sentence 1
Early airships used hydrogen as a lifting gas because it is lighter than air, but the fire risk eventually led to its replacement by helium.
Example Sentence 2
Maintenance crews stored the hydrogen cylinders in a ventilated area away from sparks.