$(i)$ The elements of the second period along with their atomic numbers in parentheses are given below: $B(5)$,$Be(4)$,$O(8)$,$N(7)$,$Li(3)$,$C(6)$,$F(9)$.
$(a)$ Arrange them in the same order as they appear in the periodic table.
$(b)$ Which element has the largest and smallest atom?
$(ii)$ Why does the atomic radius change as we move from left to right in a period?

(A) $(i)$ $(a)$ The correct order of elements in the second period is: $Li(3), Be(4), B(5), C(6), N(7), O(8), F(9)$.
$(b)$ The largest atom is Lithium $(Li)$ and the smallest atom is Fluorine $(F)$.
$(ii)$ As we move from left to right in a period,the atomic radius decreases. This happens because the nuclear charge increases with the addition of protons in the nucleus,which exerts a stronger pull on the valence electrons,drawing them closer to the nucleus and thereby reducing the atomic size.