Why won't a chain reaction occur in natural uranium?

a.) There is too much U-235 in nature to reach a critical mass.
b.) Uranium is not found in nature. We create it in laboratories.
c.) Uranium is too rare in nature.
d.) Most natural uranium is U-238, which will not go through fission easily.

Question

Why won't a chain reaction occur in natural uranium?
 	
a.) There is too much U-235 in nature to reach a critical mass.
b.) Uranium is not found in nature. We create it in laboratories.
c.) Uranium is too rare in nature.
d.) Most natural uranium is U-238, which will not go through fission easily.

anonymous · Answer

To get a chain reaction, need to concentrate U-235, which is small fraction of natural uranium ores. U-238 inhibits reaction.

shamim · Answer

chain reaction needs neutron.

anonymous · Answer

Chain reaction needs to produce more neutrons than are absorbed.

anonymous · Answer

i think its b