Arrange giving reason the following elements in increasing order of their atomic size :
(a) Be, O, F (Given that they beiong to 2nd, 16th and 17th groups respectively and to 2nd period).
(b) I, CI, F (Given that they belong to 5th, 3rd and 2nd periods respectively of 17th group).
(c) Mg, N, P (Given that Mg and P belong to `2^(nd)" and "15^(th)` group respectively of `3^(rd)` period and N belongs to `15^(th)" group of "2^(nd)` period).

Explanation

(a) All these elements are present in the `2^(nd)` period but in different group. The increasing order of their atomic radius is : `FltOltBe.`
(b) These elements are present in the same group but in different periods. Since the atomic size increases down the group `(2^(nd) , 3^(rd)" and "5^(th) "periods")` the increasing order of atomic radius is : `FltClltI`
(c) On similar line, the increasing order of atomic radius is : `NltPltMg.` For more clarification, please consult Long Form of Periodic Table.