Answer:
.5 kg
Step-by-step explanation:
At the start of Uranium-235 there is a total of 1 kg. Uranium-235 half life is 700 million years, take 1kg ÷2 = 0.5kg after 1 half life.
Let's say another 700 million years go by that means you take 0.5kg and divide that by 2.
0.5kg÷2= 0.25 kg is left after 2 half lives.
Hope this helps good luck!