4. d and f- block elements — Chemistry STD 12 Science — Question

Correct option is B. scandium

The $d-b l o c k$ elements that are the elements from a group $3-12$ are called transition elements. This is because their physical and chemical properties are intermediate between $s-b l o c k$ and $p-$ block properties. Hence these elements act as a bridge from $s-b l o c k$ to $p-b l o c k$ and hence they are known as transition. They have several oxidation states. They usually form colored compounds. An atomic number of these metals is from $21-30,39-48,57,72-80,89$, and $104-112$.

$\because$ The First main series of Transition elements starts with Scandium(Atomic no $=21)$ end with $\operatorname{Zinc}($ Atomic no $=30)$

$\therefore$ The first element of transition element is Scandium