Answer: Option (d) is the correct answer.
Step-by-step explanation:
In a group, on moving down from top to bottom there occurs an increase in atomic size due to addition of electrons into the new shells of elements.
For example, lithium and sodium are same group elements. Atomic radius of lithium is 182 pm and atomic radius of sodium is 227 pm.
Whereas when we move across a period then there occurs a decrease in atomic radius of the atoms due to addition of electrons into the same shell.
Therefore, we can conclude that the statement atomic radius increases from top to bottom within a group, is true.