- 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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The following data are observed
| $[X_2]$ | $[Y_2]$ | Rate of appearance of $XY$ ($M/sec$) |
| $0.1$ | $0.1$ | $5 × 10^{-6}$ |
| $0.2$ | $0.1$ | $10^{-5}$ |
| $0.2$ | $0.2$ | $4 × 10^{-5}$ |
Rate constant of reaction will (in $M^{1-n}\,sec^{-1}$) where $'n'$ is order of reaction
