Question

What are eka-boron, eka-aluminium and eka-silicon?

Answer 1

Hint : When Mendeleev proposed his periodic table, he left spaces in the table and predicted that then unknown elements existed with properties that were appropriate to fill those gaps. He then named them eka-boron, eka-aluminium and eka-silicon.

Complete Step By Step Answer:
Eka-boron was the name given by Mendeleev to the undiscovered element which now exists by the name of scandium. Scandium is a rare earth metal of group $3$ of the periodic table. Its atomic number is $21$ with the symbol $Sc$ .It is a silvery white metallic d-block element.
Eka-aluminium was the name given by Mendeleev to the undiscovered element which now exists by the name of Gallium. Gallium belongs to group $13$ of the periodic table. Its atomic number is $31$ with the symbol $Ga$ .It is a soft, silvery metal at standard temperature and pressure.
Eka-silicon was the name given by Mendeleev to the undiscovered element which now exists by the name of Germanium. Germanium belongs to group $14$ of the periodic table. It is known as metalloid as it has properties of both metals and non-non-metals. Its atomic number is $32$ with the symbol $Ge$ .It is lustrous, hard -brittle grayish white.
Hence, we can conclude that eka-boron is scandium, eka-aluminium is gallium and eka-silicon is germanium.

Note :
Mendeleev named the elements as eka boron because this element lies below boron, eka aluminium as this element lies below aluminium and eka-silicon as this element lies below silicon. Mendeleev named these unknown elements using the terms eka from the ancient Indian language of Sanskrit which means $1$ .