question_answer

  (a) Where is the mass of atoms concentrated? (b) Name two elements with same number of protons and neutrons. (c) Draw the atomic structure of sodium atom.

Answer:

   (i) Element electronic distribution (ii) The number of electrons in the outermost shell of element A is 8. The outermost shell of this element is complete and the element does not gain or lose electrons to complete its outermost shell. Hence, A is an inert gas.                                   (iii) Valency of element C (2, 8, 2) is 2.