Question

The number of occupied subshell in $C{r^ + }$ is:
A. 3
B. 4
C. 7
D. 6

Answer 1

Hint: This question is from the topic of electronic configuration of elements. We need to write the electronic configurations of elements according to the rules like Aufbau principle, Hund’s rule and Pauli’s exclusion principle.

Complete step by step answer:
Chromium is an element present in the d-block of the periodic table. The atomic number of Chromium is 24. Therefore, the number of electrons present in the Chromium is 24. Then, the electronic configuration of Chromium is$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^5}4{s^1}$. In the question, it is asked about the $C{r^ + }$which means one electron is released from its subshell. So, the resulting electronic configuration of $C{r^ + }$ will be$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^5}4{s^0}$. It is clear that the 4s subshell of $C{r^ + }$will be vacant and the occupied sub-shells are 1s, 2s, 2p, 3s, 3p and 3d. So, the number of occupied subshells is 6.

The correct option is D.

Additional Information:
Aufbau principle states that electrons are filled in the atomic orbitals in the increasing order of orbital energy level. The Pauli Exclusion Principle states that no two electrons in an atom can have the exact same quantum numbers. According to the Hund’s rule, before the pairing of electrons in any orbitals, every orbitals in the sub level is singly occupied.

Note:
The Chromium has an exceptional electronic configuration in the periodic table. While writing the ground state configuration of Chromium, The 4s subshell has only one electron. This is due to the exceptional stability of half-filled d-orbital in the chromium.