It will likely give up its valence electron to the other compound, forming stable octets on each of the newly formed ions. These ions have opposing charges, and tend to form strong ionic lattices. A good example of this is NaCl, which contains Na+ ions that have given up their one valence electron and Cl- ions which have accepted that electron. Hope this helps!
13.4 billion years is 3 times of the half-life, 4.47 billion years. So the Uranium-238 will go through three times of half decay. So the remain percentage will be 50%*50%*50%=12.5%.
