Which of the following elements is known as the eka-boron?

Correct option is D

The correct answer is (d) Scandium.
· Scandium was historically referred to as eka-boron before it was discovered. This nomenclature comes from Dmitri Mendeleev’s predictions using his early versions of the periodic table. Mendeleev predicted several elements' properties before they were discovered, using the prefix "eka-" (Sanskrit for "one") to indicate one place down from a known element. In this case, eka-boron referred to an element one place down from boron, which Mendeleev predicted would have similar properties to boron but heavier.
· When scandium was discovered in 1879 by Lars Fredrik Nilson, its properties matched closely with those predicted by Mendeleev for eka-boron, confirming the predictive power of his periodic table.