The white dwarf that remains when our sun dies will be mostly made of

Carbon and oxygen

Explanation:

White dwarfs are the stars which have used all their hydrogen and helium fuel and now exists with only carbon and oxygen in their core. Their size reduces up to one hundredth times of the size of their sun in early stages and yet they possess the same mass.

Due to loss of fuels and impact of gravity, a young star collapses on itself leading to formation of dwarf star.