Question
Which one of the following ions has the highest value of ionic radius ?
A.
$${O^{2 - }}$$
B.
$${B^{3 + }}$$
C.
$$L{i^ + }$$
D.
$${F^ - }$$
Answer :
$${O^{2 - }}$$
Solution :
$${O^{ - - }}\,{\text{and}}\,{F^ - }$$ are isoelectronic. Hence have same number of shells, therefore greater the nuclear charge smaller will be the size i.e. $$\,{O^{ - - }}\, > \,{F^ - }$$
further $$L{i^ + }\,{\text{and}}\,{B^{3 + }}$$ are isoelectronic. therefore $$L{i^ + }\, > {B^{3 + }}$$
Hence the correct order of atomic size is $${O^{ - - }}\, > \,{F^ - }\, > \,L{i^ + }\, > {B^{3 + }}$$