Which property of graphite is utilized in making electrodes ?

29 Give reasons for the following:

Blue colour of copper sulphate solution is destroyed when iron filings are added to it.

30 Name a non-metal having a very high melting point. 32 Name two non-metals which are both brittle and non-ductile. 33 Explain why, the surface of some of some metals acquires a dull appearance when exposed to air for a long time.