Question

What are the values of the quantum numbers of the 19th electron of scandium (Z = 21)?

Answer 1

Scandium is a chemical element with the symbol Sc and atomic number $21$. In the case of Scandium, there are $3$ orbits and $17$ electrons present in these orbits or shells. Distribution of electrons in shells is $2,8,$ and $7$. Electron configuration of Sc is: $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^1}4{s^2}$ $s^2$ .
Here, two electrons are in $4s$ orbital instead of being in $3d$ orbital because $4s$ orbital is having lesser energy than $3d$ orbital and $4s$ orbital also gives full-filled stability.

Complete answer:
Quantum numbers of an electron :
The First Quantum Number: Energy level or shell “n”:
The first quantum number is n telling the shell in which the electron is present. The first quantum number describes the radius the electron exists away from the nucleus. So $n = 1$ means that the electrons with this quantum number will be closest to the nucleus. $n = 2$ will be in the second layer, $n = 3$ will be in the third layer, and so on up to $n = 7$.
where,
n=$1,2,3,4$... Corresponds to shell=K,L,M,N...
The Second Quantum Number: Orbital Shape subshell, “ℓ”
The second quantum number determines the shape of the orbital, which is the location where electrons can be found in the atom. The number tells you how many nodes are in the shape, where a node is the
crossing point in the shape. So $l = 0$ has no crossing points and will be just a sphere like we expect of an atom.The second quantum number is telling the sub shell in which an electron is present.
$‘l’$ can take values from $0$ to $n - 1$
$l=0,1,2,3,4$.... Corresponds to sub shell=s,p,d,f.. sub shell.
The third quantum number, “m”:
The third quantum number, m l is used to designate orientation in space. The shape with $l = 1$ , has three shapes needed to completely fill the spherical shape of an electron cloud.The third quantum number is 'm' giving behavior of electrons in the magnetic field.
'm' can take values from $- l, - {l^1}, - {l^2},...0,1,2,....{l^{ - 2}},{l^{ - 1}},l$
The spin quantum number, “${m_s}$”:
This is the spin quantum number, ${m_s}$ . It turns out that quantum theory requires only two electrons to exist inside any single orbital, where a single orbital has its own size, shape, and orientation. So the two electrons have different spins with $\dfrac{1}{2}$ spin (up) and $- \dfrac{1}{2}$ spin (down). Spin is a property an electron exhibits when it is placed in a magnetic field. Certain values are allowed for the different quantum numbers: n, can be $1\mathop {}\limits_{} to\mathop {}\limits_{} 7$ $n = 4,l = 0,m = 0,{m_s} = \dfrac{1}{2}$ , can be ($n - 1$) to $0$ for each energy level n; m ℓ can be -ℓ to $0$ to ℓ for each subshell, ℓℓ; and spin is $\dfrac{1}{2}$then $- \dfrac{1}{2}$ for every orbital.The fourth quantum number is s. It tells the spin of an electron.
It can have two values for electron s= $\dfrac{1}{2}$ and $- \dfrac{1}{2}$
The 19th electron of scandium enters $4s$ orbital. Hence, $n = 4$
For an electron in s orbital $l = 0,m = 0$.
Hence, the values of the quantum numbers of 19th electron of scandium are
$n = 4,l = 0,m = 0,{m_s} = \dfrac{1}{2}$
And hence the correct answer is $n = 4,l = 0,m = 0,{m_s} = \dfrac{1}{2}$

Note:
Scandium has relatively few uses. Some scandium, however, is added to aluminum and magnesium alloys to strengthen them. Theoretically, scandium could replace aluminum as a structural material.