Answer to Question 1
Hydrogen.
Answer to Question 2
Once the usable hydrogen fuel is all burned up, there remains a helium-rich core. Once fusion is finished in the star's core, there is insufficient pressure to prevent collapse due to gravity, and the contraction generates a huge increase in internal temperature, triggering a higher level of hydrogen fusion in the star's shell. The outer shell expands from the heat of accelerated fusion, but this expansion simultaneously cools the star's surface, yielding a large, cool star.
False-color imagery of the Sun, a G-type main-sequence star, the closest to Earth.
A warning sticker on an E85 pump warning to only use this fuel in vehicles designated as flexible ...
A demand delivery system uses a fuel-pressure regulator attached to the fuel pump assembly inside ...
Hormonal Regulation of Fuel Metabolism
Evolutionary Stages of Stars
Sequence Series Arithmatic Progression Problem