Why does atomic size decrease as we move from left to right along a period in the periodic table?

Nitrogen (atomic number $7$) and phosphorus (atomic number $15$) belong to group $15$ of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Arrange the following elements in the order of their increasing non-metallic character: $Li, O, C, Be, F$.

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?

Atomic radii of the elements of the second period are given below :

Period $II$ elements	$B$	$Be$	$O$	$N$	$Li$	$C$
Atomic radius $(pm)$	$88$	$111$	$66$	$74$	$152$	$77$

$(i)$ Arrange them in decreasing order of their atomic radii.
$(ii)$ Are the elements now arranged in the pattern of a period in the Periodic Table?
$(iii)$ Which elements have the largest and the smallest atoms?
$(iv)$ How does the atomic radius change as you go from left to right in a period?

Which among the following elements has the largest atomic radii?