Which one of the following is the correct electronic configuration of sodium?

Rutherford's alpha-particle scattering experiment was responsible for the discovery of

Compare all the proposed models of an atom given in this chapter.

If bromine atom is available in the form of,say,two isotopes $_{35}^{79}Br$ $(49.7 \%)$ and $_{35}^{81}Br$ $(50.3 \%),$ calculate the average atomic mass of bromine atom. (in $,u$)

If the number of electrons in an atom is $8$ and the number of protons is also $8$,then $(i)$ what is the atomic number of the atom? and $(ii)$ what is the charge on the atom?

If $Z = 3$,what would be the valency of the element? Also,name the element.