Q.Which of the following is an element whose existence was predicted by Mendeleev and discovered later?

Mendeleev's periodic table left blank spaces for elements not yet discovered; 'eka-aluminium', predicted from the properties of aluminium and its neighbours, turned out to be gallium.

While arranging known elements by increasing atomic mass into groups of similar properties, Mendeleev found some positions in his table had no known element to fit — rather than force-fit a wrong element, he left the space blank and predicted the properties the missing element should have, based on the trend of the elements around it.

He named these gaps using the prefix 'eka' (Sanskrit for 'one') attached to the preceding element in the same group, e.g. 'eka-aluminium' (below aluminium), 'eka-silicon', and 'eka-boron'.

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