[Shahab Mirza]

The quantum number n denotes the successive electron shells, so n=1 is K, n=2 is L, n=3 is M, n=4 is N and so on.
Corribus has already given the best answer to this question, I don't see what else I can say.
The question is probably alluding to the fact that e.g. for potassium the electron configuration is 1s²2s²2p⁶3s²3p⁶4s¹, i.e. the outermost electron goes in 4s (answer B) rather than 3d (answer A) as might be expected. In this case then, A is the higher energy. But the relative energy of these orbitals varies with atomic number.

sir listen, corribis said this
"For a multi-electronic atom, this changes because the l quantum number impacts energy (due to penetration and shielding effects). Here we're basically being asked what fills first: the 3d or 4s orbital when putting multiple electrons into hydrogenic orbitals. The 3d is usually filled first"
now i just want to know that what is relations betwwen 3d orbital and l quantum number how we know?

[Shahab Mirza]

The quantum number n denotes the successive electron shells, so n=1 is K, n=2 is L, n=3 is M, n=4 is N and so on.
Corribus has already given the best answer to this question, I don't see what else I can say.
The question is probably alluding to the fact that e.g. for potassium the electron configuration is 1s²2s²2p⁶3s²3p⁶4s¹, i.e. the outermost electron goes in 4s (answer B) rather than 3d (answer A) as might be expected. In this case then, A is the higher energy. But the relative energy of these orbitals varies with atomic number.

sir listen the corribis said that
"For a multi-electronic atom, this changes because the l quantum number impacts energy (due to penetration and shielding effects). Here we're basically being asked what fills first: the 3d or 4s orbital when putting multiple electrons into hydrogenic orbitals. The 3d is usually filled first"

i want to know that what is relation between 3d and l quantum number?

[Shahab Mirza]

The quantum number n denotes the successive electron shells, so n=1 is K, n=2 is L, n=3 is M, n=4 is N and so on.
Corribus has already given the best answer to this question, I don't see what else I can say.
The question is probably alluding to the fact that e.g. for potassium the electron configuration is 1s²2s²2p⁶3s²3p⁶4s¹, i.e. the outermost electron goes in 4s (answer B) rather than 3d (answer A) as might be expected. In this case then, A is the higher energy. But the relative energy of these orbitals varies with atomic number.

Thank you all , Sir its good for me that I reviewed corribis's answer and came to knew that he was right as he said that the in case of multielectrons l matters because of high penetrating power it affects energy thats why in the answer l=2 means more enrgy and hence is answer , right? was this the thing in which i was confusing.?

[mjc123]

Yes. For electrons in the same shell, the s orbital (l=0) is more penetrating than the p orbital (l=1), so feels more of the nuclear charge, and has lower energy. Similarly p is lower energy than d (l=2), and so on. For the higher shells, these ranges of orbital energies overlap, so e.g. 4s is lower than 3d.

[Corribus]

@Shahab Mirza

Maybe this Chemguide page will help.

http://www.chemguide.co.uk/atoms/properties/3d4sproblem.html

[Shahab Mirza]

Thanks all of you , you are doing a good thing Sir helping students in education and all that is amazing , hats off , and thanks alot once again , Sir MJC123 and Sir Corrobis . I understood this concept , it will also help me to solve other related such problems =D

[AdiDex]

In short you Can do these kind of question by Aufbau Principle ,

which electron have greater value of n+l , its energy will be higher.
 1. n = 3 , l = 2 , then n+l = 5
 2. n=4. , l= 0. , then n+l = 4

BTW Bro , dont call me sir , i am in High school , i think i'm your junior as you said that you have passed high school.