Final answer:
It is true that there is very little hydrogen in Earth's atmosphere because its lightness allows it to escape into space over time. Hydrogen in Earth is mainly found in water and organic compounds, and the atmosphere contains only a trace amount of free hydrogen.
Step-by-step explanation:
The statement is true. Hydrogen gas is indeed very light - with a molecular weight of approximately 1 - allowing it to escape Earth's atmosphere over time. This process has led to hydrogen being nearly absent in the atmosphere currently. Furthermore, because hydrogen is so light, it reaches higher speeds than heavier gas molecules like nitrogen and oxygen. As a result, it is more likely that hydrogen molecules achieve speeds greater than Earth's escape velocity, which is roughly 11 km/s, thereby escaping into space. This phenomenon has contributed to the current scarcity of free hydrogen in the atmosphere. On Earth, hydrogen is primarily found in association with oxygen as water (H2O), and is also locked up in organic compounds. The atmosphere's partial pressure of H2 is less than 1 atm, signaling its limited presence in the Earth's atmosphere.