Question

The atomic number $Z$ of an element is $25$ . In its ground state, how many electrons are present in the N shell?
A. $13$
B. $2$
C. $15$
D. $3$

Answer 1

The ground state of an atom is the state of that atom in which the electrons are present with their maximum energy values and still be the part of an atom. In simple words, ground state of an atom is the state just before the electrons lose their energy and the atom gets ionized

Complete answer:
To find the number of electrons in the N shell, we need to find the electronic configuration of the atom as per following rules:
Rule-1: Aufbau Principle: It states that the electrons must be filled first in the orbitals which are associated with the lower energy values. It can be determined using the expression n+l, where n is the principal quantum number whereas l is the azimuthal quantum number.
Rule-2: Pauli’s Exclusion principle: It states that only two electrons can be filled in a single orbital and they must have opposite spin. For example, if one electron in the orbital is oriented clockwise, then it is mandatory to position the second electron anticlockwise.
Rule-3: Hund’s rule: It states that all the orbitals of the same energy level must be singly filled before the pairing of electrons takes place.
Keeping all these rules in mind, the noble configuration of the given atom is as follows:
$[Ar]3{d^5}4{s^2}$
The N shell is associated with the fourth energy level i.e., for the N shell, the value of the principal quantum number is $4$ .
Therefore, the number of electrons present in the N shell of the given atom is $= 2$ .

Note:
The chemical element associated with atomic number $25$ is manganese. It is a transition metal which has the tendency to show the highest number of variable oxidation states. The most common oxidation states of Manganese are $+ 2$ , $+ 3$ , $+ 4$ , $+ 6$ and $+ 7$ .