One of the following is not an allotrope of carbon. This is:

48 A diamond-toothed saw is usually used for cutting: 49 The organic compound prepared by Wohler from an inorganic compound called ammonium cyanate was: 51 The number of carbon atoms in the organic compound named as 2, 2-dimethylpropane is: 52 The pair of elements which exhibits the property of catenation is: