Question

Electrons should be filled in the various shells one by one in the order of increasing energy according to _____rule

• A.
  $2n$
• B.
  $n^2$
• C.
  $2n^2$
• D.
  $n+1$

Answer 1

The correct option is C

$2n^2$
Electrons are filled in the various shells according to the $2n^2$ rule.

For example: ${}_8^{16}O$ has 8 protons , based on the $2n^2$ rule, the electrons in the shells are represented as 2,6

For the $1^{st}$ shell, the number of electrons that can be accommodated are $2(1{)}^2=2$

For the $2^{nd}$ shell , the number of electrons that can be accommodated are $2(2{)}^2=8$

Maximum of 8 electrons can be accommodated for the oxygen atom .As 2 electrons are already accommodated in the first shell only 6 electrons can be accommodated in the second shell.