- 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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Assertion $(A)$: There is a considerable increase in covalent radius from $\mathrm{N}$ to $\mathrm{P}$. However from $As$ to $Bi$ only a small increase in covalent radius is observed.
Reason $(R)$: covalent and ionic radii in a particular oxidation state increases down the group.
In the light of the above statement, choose the most appropriate answer from the options given below:
$Pt\,|\,B{r_{2(\ell )0.1M}}\,|\,Br_{({\text{aq}}),0.1M}^ - \,||\,H_{_{({\text{aq}})0.1M}}^ + \,|\,{H_{2(g)1atm}}\,|\,Pt$ given ; $E_{B{r^ - }/B{r_2}}^0\, = \, - 1.06\,V$