Question

The group number and period of the chromium in the periodic table are, respectively:
(A) 6 and 3
(B) 5 and 3
(C) 6 and 4
(D) 5 and 4

Answer 1

Hint: An attempt to solve this question can be by writing down the electronic configuration of the element. After this you can identify the group and period using the principal quantum number and the orbital in which the last electron takes place.

Complete step by step answer:
Let us write down the electronic configuration (e.c.) of chromium in its ground state. The atomic number of chromium is 24.
Electronic configuration of Z=24 is,
$1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{4}}$

Valency is defined as the number or electrons that need to be gained or lost in order to gain maximum stability of the radical. Chromium can show multiple valences as the energy between 4s subshell and 3d subshell is very less and can thereby easily lose electrons.
The highest principal quantum number in which the electrons are present for the element with atomic number(Z=24) is 4. The period of the element is 4.
The last electron goes into the d subshell while writing the electronic configuration. So, the element belongs to the d block.
Since 4 electrons are filled in the d subshell. The group number becomes (2+ 4) = 6.
So, the correct answer is “Option C”.

Note: The above electronic configuration for chromium is valid only to determine the group and period. The stable electronic configuration has 5 electrons in the 3d subshell and only 1 electron in the 4s subshell. This is in accordance with Hund's rule for maximum multiplicity.
Electronic configuration of Z=24 is,
$1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}4{{s}^{1}}3{{d}^{5}}$