I found a similar question, so I think this can be taken as our problem because you seem to forgot including the picture. So, for letter a, the answer is: they represent different compounds. As you can notice, the CH₂CH₃ and CH₃ are both on the top side for the left figure, while the CH₃ and CH₃ are on the top side of the right figure. They are cis-trans isomers. The left figure is trans-2-pentene while the left figure is cis-2-pentene.
Fission. When a large fissile atomic nucleus such as uranium-235 or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, (the fission products), releasing kinetic energy, gamma radiation, and free neutrons.
Answer: they are held together by hydrogen bonds I believe
Explanation:
Bohr's original model stated that electrons were tiny little objects circling the nucleus along fixed orbits, however this is no longer valid as we now know that rather "circling" the nucleus at confined orbits, electrons can seem to be everywhere at once.