Question

In Boron atom, shielding of the last electron is due to

• A.
  electrons of K shell only
• B.
  all the electrons of K and L shells
• C.
  two electrons of 1s and 2s each
• D.
  all the electrons of the L shell only

Answer 1

The correct option is C

two electrons of 1s and 2s each
Electronic configuration of Boron:
$1s^{2}2s^{2}2p^1$

The last electron of Boron is shielded by two electrons of K shell and two electrons of L shell.