Question

Consider the ground state of $ Cr\left( {Z = 24} \right) $ .The no. of electrons with the azimuthal quantum no. $ l = 1 $ and $ 2 $ respectively are-
 $ \left( A \right)16\& 4 $
 $ \left( B \right)12\& 5 $
 $ \left( C \right)12\& 4 $
 $ \left( D \right)16\& 5 $

Answer 1

Hint: The ground state of any element is the lowest energy level. When atoms absorb energy they move on to higher levels and these are known as excited states. The quantum numbers of electrons define the exact location of electrons. The azimuthal quantum number gives us the information of the number of subshells the electron is present.

Complete answer:
 The atomic number of Chromium is 24, the electron configuration of Chromium is $ 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1}3{d^5} $
The azimuthal quantum number $ l $ has values as

Value of $ l $	The subshell it represents
0	s
1	p
2	d

The electrons in the ground state of Chromium with azimuthal quantum $ l = 1 $ and $ 2 $ correspond to subshells p and d respectively.
From, the electron configuration of Cr the number of electrons in $ l = 1 $ which corresponds to the subshells p will be equal to the sum of electrons in $ 2{p^6} $ and $ 3{p^6} $ subshells which is equal to $ 6 + 6 = 12 $
And from the electron configuration of Cr the number of electrons in $ l = 2 $ which corresponds to the subshells d will be equal to the number of electrons in $ 3{d^5} $ which is equal to 5.
Therefore, the number of electrons in the azimuthal quantum number $ l = 1 $ and $ 2 $ are 12 and 5 respectively.
Option $ \left( B \right)12\& 5 $ , is the correct choice among the options.

Note:
The principal quantum number (n) represents the shell (K, L, M, N) in which the electron is present. And the value of azimuthal quantum number $ l $ depends on n , $ l = n - 1 $ . Which means that the first shell can have one subshell, the second shell can have two subshells.

Shell number (n)	The no subshell	Azimuthal quantum no.	Shape of subshell
1	1	0	s
2	2	0,1	s, p
3	3	0,1,2	s, p, d