Mendeleev left gaps in his table and named three undiscovered elements eka-boron, eka-aluminium and eka-silicon. These were later identified respectively as:

1. Mendeleev predicted properties for the gaps next to known neighbours. 2. Eka-boron later turned out to be scandium (Sc). 3. Eka-aluminium later turned out to be gallium (Ga). 4. Eka-silicon later turned out to be germanium (Ge). 5. So the correct order is scandium, gallium, germanium. 6. Rule out the others, which scramble this fixed naming order. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 2 "Periodic Classification of Elements", p.28_