- AChromium
- ✓Scandium
- CNickel
- DCopper
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
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$(A)$ $P$ can be reduced to a primary alcohol using $NaBH _4$.
$(B)$ Treating $P$ with conc. $NH _4 OH$ solution followed by acidification gives $Q$.
$(C)$ Treating $Q$ with a solution of $NaNO _2$ in aq. $HCl$ liberates $N _2$.
$(D)$ $P$ is more acidic than $CH _3 CH _2 COOH$.

