The total lifetime of the sun is about 10 billion years, from when it was born to when it dies, and the half-life of 238u is 4.5 billion years. suppose a particular meteoroid contained 24 micrograms of uranium-238 (238u) when the sun was born. if the meteoroid is still in orbit when the sun dies, it will contain

a little less than 6 micrograms

Explanation:

The half-life of an element is defined as the time in which half of the isotope emits its radiation and becomes a different element. Therefore after 4.5 billion years the meteoroid will contain 12 micrograms of uranium,  after 9 billion years will contain 6 micrograms. After 10 billion years will contain a little less than 6 micrograms.

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask

thermal energy is the answer