How does atomic size varies along the period and down the group in s-block elements?

Explanation

(i) Variation along the period: In s-block elements, when we move from left to right in a period atomic size goes on decreasing. This is due to the increase in effective nuclear charge.
(ii) Variation down the group: In s-block elements, on moving down the group, atomic size goes on increasing. this is due to the increase in the principal quantum number (n).