15. Which of the following is used as a lubricant in heavy machines? A.Bauxite B.Sulphur C.Phosphorus D.Graphite
Answer: Option D Solution: Graphite is used as a lubricant in heavy machines. it is made of carbon atoms arranged in sheets of hexagonal units - looks a lot like chicken-wire. Another sheet forms on top of this and so on. There is no proper connection (in ideal graphite) between the sheets, so they are able to slide freely over each other without breaking any bonds.
