Which of the following is the smallest in size ?
1. N3-
2. O2-
3. F-
4. Na+

Your friend Ajit is correct.
All the given species contain 10 electrons. 
Species with maximum number of proton will attract the electrons strongly towards it and will be smallest in size.
The number of proton in each species are as follows :
1.N3- = 7 protons
2. O2- = 8 protons
3. F- = 9 protons
4. Na+ = 11 protons
(Number of protons = atomic number)
Na+ with maximum number of protons will be smallest in all.

 

  • 8
O2
  • -3
Na+IS SMALLEST IN SIZE.
THIS IS BECAUSE ALL THE GIVEN IONS ARE ISOELECTRONICSO THE HAVE SAME NUMBER OF ELECTRONS BUT SODIUM ION HAS MAXIMUM NUMBER OF PROTONS SO IT WILL ATTRACT ELECRONS MORE EFFICIENTLY
  • 1
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