Step 1: Mendeleev named the predicted elements by adding "eka" (meaning "one") to the name of the element just above the gap in the same group. Step 2: Eka-aluminium was predicted below aluminium (Group III). It was discovered in 1875 and named gallium; its properties (low melting point, atomic mass about 69.7) matched his prediction. Step 3: Scandium was eka-boron and germanium was eka-silicon; these were also predicted by him. Step 4: Boron lies above aluminium, so it cannot be eka-aluminium. Answer: Gallium.