Answer:
4,500 million years is the half-life of U-238.
Explanation:
A is correct because as we can see from the graph, U-238 has lost about half of its mass over the course of 4,500 million years, thus that is its half-life.
B is not correct because by 9,000 the U-238 has only kept about 28% of its original mass.
C is not correct because in 4,500 years the U-238 is barely changed, and it still has almost all of its initial mass.
D is not correct because in 50 million years the U-238 has only lost slightly more than 1% of its initial mass.
