Answer: Option (b) is the correct answer.
Explanation:
As it is known that when we move across a period then size of atoms decreases due to addition of electrons into the same sub-shell.
As a result, force of attraction between the nucleus of the atom and its electrons increases due to which there will be shrinkage in the size of atom.
But when electrons add into the same orbital then there will be electron-electron repulsion. As a result, size of the atom tends to increases.
This increase in size will be compensated by the attraction of electrons by the nucleus of the atom.
Thus, we can conclude that atomic radius remains almost unchanged as you move through Period 2 from Group 14 to Group 18 because the repulsion between electrons becomes equal to the attraction of the nucleus for the electrons.