A physical change is classified as a change that does not affect the identity of the substance. Otherwise, that would be a chemical change. From the picture above, you will know that it is a chemical change if the colored circles combined with a different color. You will know if it's a physical change if there is only separation of the same colors. The answers are shown in the picture attached.
Compound A will be 2-chloro-butane which in the presence of sodium methoxide will undergo the elimination of the halogen with a hydrogen from the neighboring atom carbon (not the one with which the halogen in bound), which have less hydrogen atoms, forming the trans-2-butene.
Answer:
Removing the dirty water and replacing with fresh water. also the fish containing in the aquarium change the system of aquarium.
Answer:
atoms of different elements combine and form new elements