hydrogen
A neutron star is already the remains of a massive star that has run out of fuel.
Neutron stars do not have fuel. A neutron star is a remnant of a star that has already died.
a dwarf star
A typical star starts out with a lot of hydrogen-1. This is the star's fuel, which is gradually converted into helium-4, and in some cases, into heavier elements.
For most of a star's life, the main fuel is protium (hydrogen-1), which is fused into helium-4.
When a star has burnt up all of its fuel and energy, it will collapse.
Yes. A white dwarf is a compact star, the remnant of a star that has run our of fuel.
Usually the fact that the star runs out of fuel.
A star, after using all of it's fuel explodes. We call this a super nova, and after this the star will either become a black dwarf star (or maybe a white dwarf) or it will collapse in on its self creating a black hole.
When a Star runs out of fuel, it will expand into what is known as a "Red Giant". Massive stars will become "Red Supergiants". This phase will last until the star exhausts its remaining fuel. At this point, the pressure of the nuclear reaction is not strong enough to equalize the force of gravity and the star will collapse. Go to related link to read more about Stars... ;)
When the star's fuel source depletes and the nuclear reaction inside the star cannot resist the pull of gravity any more. The constant explosion in the star would want to expand but gravity of the star keeps it in the shape of a sphere. So when the fuel for the nuclear reaction has been used up, it will get pulled in by the force of gravity. To answer the question: it depends on what type of large star you are talking about, how much fuel it has, and how long it takes for that star to burn up its fuel.
It is inside of the fuel tank.