Question

Define atomic size of an element.

Atomic radii of some elements like C, Li, N, O, B and Be are 77, 152, 74, 66, 88 and 111 pm respectively.

Rearrange them in decreasing order of their atomic radii.

Name the elements which have largest and the smallest size respectively.

Give reason for the change in atomic radius as you move from left to right in a period.

Answer 1

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As atomic size increase on the increase in radii 

decreasing order of their atomic radii : 

152pm > 111pm > 88pm > 77pm > 74pm > 66pm 

Largest size = 152 pm = Li 

smallest size = 66 pm  = oxygen 

On Moving left to right Atmoic radius is generally decreases because the electron add in same shell 
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Answer 2

the distance from the centre of the nucleus to the outermost shell containing electrons.
Li>Be>B>C>N>O.
largest is Li and smallest is O.
As electronegativity increases.