Question

Which of the following is a transition element?
A. $Al$
B.$As$
C.$Ni$
D.$Rb$

Answer 1

Transition elements are those elements which are placed between metals and non - metals in periodic table. They are also called d-block elements.

Complete step by step answer:
Let us first explain the periodic table.
According to modern periodic table given by Moslay:
Non - Metals are placed in group $13$ to group $17.$Inert gases are placed in group 18. And transition elements are placed in group 3 to group 12.
Aluminum$(Al)$ belongs to group $3.$ Therefore, it is metal.
Arsenic$(As)$ belongs to the group $15$ therefore it is metalloid.
Rubidium $({R_b})$ belongs to group $1$. Therefore, it is metal.
Nickel $(Ni)$ belongs to group $10$, therefore it is transition metal.

So, the correct answer is “Option C”.

Additional information:
The Atomic Number of $Ni$ is $28.$
It’s electronic configuration is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^8}4{s^2}.$
$= [Ne]3{s^2}3{p^6}3{d^8}4{s^2}$.
Since Electronic configuration of $Ne$ is $1{s^2}2{s^2}2{p^6}$. Therefore, we can write $Ne$ in place of $1{s^2}2{s^2}2{p^6}$.

The energy of $4s$ orbital is less than $3d$ orbital therefore electron enters in $4s$ orbital first and then $3d$ orbital therefore electron enters in us first and then $3d.$ Thus last electron in Nickel enters in $d -$ orbital. Therefore, it is known as $d - block$ elements.

Note:
There are four transition series called as first (4d), second (5d), third (6d) and Fourth (7d). Nickel belongs to the first transition series.
Transition element can be identified by filling electrons in the orbital. If the last electron enters in $d -$orbital it is a transition element. Electrons should be filled according to Aufbau principle.