From a study of properties of neighbouring elements, the properties of an unknown element can be predicted - justify with an example.

Explanation

Mendeleev left some gaps in the periodic table. He predicted the properties of these unknown elements after studying the properties of the neighbouring elements. When he proposed the periodic table. The elements scandium (Z = 21) , gallium (Z = 31) and germanium (Z = 32) were unknown. Not only he predicted their properties but also named them eka-boron, eka-aluminium and eka-silicon respectively. The three elements were soon discovered within 20 years of his pronouncement of the 'periodic law' (during his life time). It is astonishing to see that when the properties of these elements were studied, these showed a remakable agreement with those predicted by Mendeleev.
In addition to the above three elements, Mendeleev the discovery of some more elements:
Examples:
`{:(S.NO.,"properties of Eka-silicon predicted by Mendeleev(1871)","Properties of Germanium discoverved by Winkler(1886)"),(1.,"Atomic weight"72,"Atomic weight"72.6),(2.,"Specific gravity"5.5,"Sp.gravity"5.46),(3.,"Colour-dirty grey","Colour-greyish white"),(4.,"Specific heat 0.073","Specific heat 0.076"),(5.,"Oxide"-EsO_(2)"less basic than"SnO_(2)",but more basic than"Si_(2)OSp.gr.4.70",refractory","Oxide"-GeO_(2)",slightly basic SP.gr."4.70", refractory"),(6.,"Chloride"-EsCl_(4) a "liquid, B.P. below"100^(@)C,"Chloide"-GeCl_(4)",liquid B.P."86.5^(@)C):}`.