Science
The first and lightest element of the Periodic Table
Hydrogen
The only continent with no countries
Antarctica
The particle that makes up all matter
Atom
The country with the largest population
India
The term that describes the theory of life arising from inanimate material
Abiogenesis
An isolated, safe, peaceful, and cold island nation which has never been involved in a war since its independence
Iceland
The most volcanically active body in the solar system
Io, a moon of Jupiter
The most densely populated island in the world (with a substantial amount of citizens, at least)
Malé, ~94,200 people per square kilometer. Also the capital city of the Maldives
Measuring the redshifting and blueshifting spectrum of light from a star due to wobbling back and forth from our perspective because of the gravitational effects of an orbiting planet to detect said planet
What Maryland and Yemen have in common
Having no natural lakes