What is meant by 'group' in the modern periodic table? How do the following change on moving from top to bottom in a group?
$(i)$ Number of valence electrons
$(ii)$ Number of occupied shells
$(iii)$ Size of atoms
$(iv)$ Metallic character of elements
$(v)$ Effective nuclear charge experienced by valence electrons.

(N/A) group is defined as the vertical column of elements in the modern periodic table.
$(i)$ The number of valence electrons remains the same for all elements in a group.
$(ii)$ The number of occupied shells increases by one as we move down a group.
$(iii)$ The size of atoms increases because the number of shells increases,leading to a greater distance between the nucleus and the outermost electrons.
$(iv)$ The metallic character of elements increases as we move down a group because the tendency to lose electrons increases due to the increased atomic size.
$(v)$ The effective nuclear charge experienced by valence electrons decreases as we move down a group because the distance between the nucleus and the valence electrons increases,and the inner shells provide more shielding.