Question

Which of the following sequence is correct as per Aufbau principle?

• A. $ 35\text{ }<\text{ }3d\text{ }<\text{ }45\text{ }<\text{ }4p $
• B. $ 1s\text{ }<\text{ }2p\text{ }<\text{ }4s\text{ }<\text{ }3d $
• C. $ 2s\text{ }<\text{ }55\text{ }<\text{ }4p\text{ }<\text{ }Sd $
• D. $ 2s\text{ }<\text{ }2p\text{ }<\text{ }3d\text{ }<\text{ }3p $

Answer 1

Answer: (B)

According to aufbau principle, "sub-shells are filled with electrons in the increasing order of their energies," i.e., sub-shell of lower energy will be filled first with electrons. Thus correct order is? $ 1s<2s<2p<3s<3p<4s<3d<4p $ $ <5s<4d<5p<6s<4f<5d<6p $ $ <7s<5f<6d...\text{ }etc. $