State in brief the drawbacks of Rutherford's atomic model correlating them with the postulates of Bohr's atomic model.

An element 'A' has mass number 23 and atomic number 11. State the —

(i) no. of neutrons in it's shell,
(ii) electronic configuration of the element 'A'.

What is meant by the terms :

(i) subatomic particles,

(ii) nucleus,

(iii) orbits,

(iv) atomic number

(v) mass number with reference to an atom.

What are 'energy levels'? Explain the arrangement and distribution of electrons in the various shells with reference to an atom in general and to an atom of potassium $^{39}_{19}\text{K}$ with special reference to the 2n² rule.