Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium. The group and period of these elements in the modern periodic table are:

 In the modern periodic table, the elements predicted by Mendeleev and named as Eka-silicon and Eka-aluminium correspond to the elements Germanium (Ge) and Gallium (Ga), respectively.

1. Eka-silicon: Mendeleev predicted an element with properties similar to silicon and placed it below silicon in his periodic table. This predicted element is now known as Germanium (Ge). In the modern periodic table, Germanium is in Group 14 (IVA) and Period 4.

2. Eka-aluminium: Mendeleev predicted an element with properties similar to aluminium and placed it below aluminium in his periodic table. This predicted element is now known as Gallium (Ga). In the modern periodic table, Gallium is in Group 13 (IIIA) and Period 4.

Both Germanium and Gallium were discovered later and found to have properties that closely matched Mendeleev's predictions, providing strong evidence for the validity of his periodic table.