Answer:
Enriched uranium-
Step-by-step explanation:
Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written ²³⁵U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (²³⁸U with 99.2739–99.2752% natural abundance), uranium-235 (²³⁵U, 0.7198–0.7202%), and uranium-234 (²³⁴U, 0.0050–0.0059%). U is the only nuclide existing in nature (in any appreciable amount) that is fissile with thermal neutrons.