What is the specific gravity (SG) of Hydrogen?

The correct option is about the specific gravity (SG) of Hydrogen being approximately 0.07 when compared to air. Specific gravity is a measure that compares the density of a substance to the density of a reference substance, typically air or water, and is dimensionless. Hydrogen is much less dense than air, which is why its specific gravity is significantly less than 1.

Hydrogen's low specific gravity means it will rise in the atmosphere, making it a very lightweight gas. This characteristic is crucial for various applications, including its use in balloons and as a potential energy source, where buoyancy plays an important role.

Other options represent specific gravity values that do not correspond with hydrogen. A value of 0.01 is not realistic for hydrogen, as it suggests an even lighter gas than hydrogen compared to air. A value of 1.0 would be indicative of a gas that is the same density as air, which does not apply to hydrogen. Lastly, a value of 1.191 is greater than 1, indicating a substance denser than air, again not applicable to hydrogen. Thus, the selected specific gravity of hydrogen aligns with its known physical properties.