What best describes the substances represented by these two diagrams?

We see that the compounds have the same atoms in their formula. However, they are not the same, because we cannot move the one on top of the other so that all atoms are the same. Specifically, the CH in the first case are not adjacent, while in the second case they are. They are constitutional isomers because they use the same chemical atoms in the same proportions, but their arrangement is different (they are not the reflection of each other too). There are examples of isomers in nature that have completely different propertie 

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explanation:

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when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.