Question

Out of O, O - and O 2- which one has smallest radius and why?????

Answer 1

o has smallest Radius because if electron increases in any atom their size also increases

Answer 2

when an atom gains electrons it form anion. In above case, O gains an electron to form 0- ions. When an atom gain an electron its nuclear charge remain same but number of electrons increases. Now nuclear charge has to act on larger number of electrons. As a result attraction between the nuclear charge and outermost electrons decreases which result in increases in size. Therefore from O to O- extra electron are added, hence size increases. From O- to O2-, one more extra electron is added which result in further decrease in attraction between the nuclear charge and outermost electron and further size increases. Therefore the decreasing order of size is
O-2>O->O