Question

The physical and chemical properties of elements belonging to the same group are similar, why?

Answer 1

The physical and chemical properties of elements of same group are similar as the elements of one group have same valency and are hence likely to be of same type (metal/non metal) and are likely to react similarly with substances.

Answer 2

becoz reactivity and physical properties predominantly depends upon the valence electron. as in groups the valency is same hence properties are also same