Have you put any thought into these or do you expect us to do your homework?
Here are some VERY limited answers. Repost if you need clarification but tell us what you don’t understand about the problem.
1.effect depends upon if the compounds are volatile or not. Look up Raoult’s law.
2. to determine the purity.
3. recheck the process. If the same thing happens, the point at which it disappears is called the decomposition point.