(N/A) We know by now that the elements are the basic units of all types of matter. In $1800$,only $31$ elements were known. By $1865$,the number of identified elements had more than doubled to $63$. At present,$114$ elements are known. Of them,the recently discovered elements are man-made. Efforts to synthesize new elements are continuing. With such a large number of elements,it is very difficult to study the chemistry of all these elements and their innumerable compounds individually. To ease this problem,scientists searched for a systematic way to organize their knowledge by classifying the elements. This not only rationalizes known chemical facts about elements but also helps in predicting new ones for further study.