The existence of which of the following elements was predicted by Mendeleev before it was actually discovered?

Mendeleev left some gaps in his periodic table for some undiscovered elements. Mendeleev boldly predicted that these elements would be discovered later. He even predicted the properties of these unknown elements and named these elements by prefixing a Sanskrit word ‘eka’ to the name of the preceding element in the same group, e.g. eka–boron for scandium, eka-aluminium for gallium and eka-silicon for germanium. Titanium, cesium and iodine were already discovered when Mendeleev gave his periodic table. So, option (1) is the correct answer.