CBSE Class 9 Answered

(a) Atomic number = 11 

     Electronic configuration = 2, 8, 1

     Atomic number = 19

     Electronic configuration = 2, 8, 8, 1

(b) The following are the observations of Rutherford's α-particle scattering experiment:

    (i) Most of the α-particles passed straight through the gold foil.

    (ii) Some of the α-particles were deflected by the foil by small angles.

    (iii) Surprisingly, one out of every 12,000 particles appeared to rebound.

                                                                     OR

(a)

(b) Maximum number of electrons in K shell = 2n²

     For K shell, n = 1

     Maximum number of electrons in K shell = 2

(c) Atoms combine with other atoms to achieve the electronic configuration of nearest noble gas and become more stable.