A) Describe the main features of Bohr's model of an atom. Draw a neat and labelled diagram of energy levels. (b) Which of the following pairs are isotopes and which are isobars?

(a) Features of Bohr’s Models :
(i) Electrons revolve in certain permitted orbits which are associated with fixed amount of energy. So they are called energy levels (K, L, M, N).
(ii) As long as electron revolves in the same energy level, they do not radiate energy.
(iii) The energy of orbit closest to nucleus is lowest and farthest away is highest.
(iv) When we supply energy to electron, it goes to higher energy level and when it comes back to lower level it radiates energy.

© B would be more reactive as its electronic configuration is 2, 8, 6 and it requires two more electrons to complete its octet.