The Turing test being a valid test of intelligence all depends. It depends on the way that the computer is built, so generally I would say that it is not a valid test of intelligence. You never know when a computer can be wrong if you yourself do not know the answer to a question, so it is (generally) not a valid test of intelligence.
2- List several mental task that people do better than computers. List several mental tasks that computers do better than people. Can you find any general characteristics that distinguish the items on the two lists?
A mental task that humans do better than computers is the feel of emotion. Since computers do not have emotion, it is obvious that a human would do this better than them. A task that a computer does better than a person would is keep the names of something (say a list of groceries). Since humans tend to forget easily, and computers never forget anything, the computer would be a better mental task holder. Generally the characteristics of computers are good memory and for humans are emotion.