Study the variation in the atomic radii of Group $I$ elements given below and arrange them in an increasing order.
$(i)$ Name the elements which have the smallest and the largest atoms.

Group $I$ elements

$Li: 52\, pm, Na: 61\, pm, K: 231\, pm, Rb: 244\, pm, Cs: 262\, pm$

$(ii)$ How does the atomic size vary as you go down a group?

(A) The increasing order of atomic radii is: $Li (52\, pm) < Na (61\, pm) < K (231\, pm) < Rb (244\, pm) < Cs (262\, pm)$.
$(i)$ The element with the smallest atom is Lithium $(Li)$ with an atomic radius of $52\, pm$, and the element with the largest atom is Caesium $(Cs)$ with an atomic radius of $262\, pm$.
$(ii)$ As we move down a group in the periodic table, the atomic size increases. This happens because a new electron shell is added to the atom at each step, which increases the distance between the outermost electrons and the nucleus, thereby increasing the atomic radius.