2. You may mean impossible where you typed possible, and I will assume that. Oxygen is the final electron acceptor in the electron transport chain for aerobic respiration. If cyanide takes the spot of oxygen in hemoglobin, then electrons have no where to go at the end of the chain. If electrons have no where to go, it clogs the chain so that the chain cannot accept any new electrons. If the chain cannot accept new electrons, then no ATP is made since energetic electrons passes their energy to ADP and phosphate to generate ATP.
3.Transporting H through the matrix lowers the proton gradient necessary to run ATP synthase. It's like a water mill. If you raise the water level so that the water coming in and water coming out are the same, then the mill won't run, or it runs very inefficiently. That's why the Hoover dam is so big.
4. Same reason as 3. The inner membrane is permeable to H , so a proton gradient can't be established to operate ATP synthase. It would be like trying to fill a bucket covered in holes.
5. Color is reflected light of a certain wavelength. The other wavelengths are absorbed by a pigment. For example, the pigment chlorophyll reflects green light, but it absorbs red and blue light. There is a good chance that organisms will have color to increase their capacity to absorb light energy from a nearby star.
Alternatively, color is also a good way to hide yourself from predators.