Name the element or compound which is associated with Hall's process.

41 Explain the displacement of hydrogen by a metal from an acid with an example. Give the equation to support the same. 42 Why is sodium kept in kerosene? 44 Which metal is used in nuclear reactors and aerospace projects? 1

A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.