Question

elements in a group of the periodic table have similar chemical properties

Answer 1

This is because elements in the same group have same number of valence electrons. Chemical properties depend on number of valence electrons. So, they have similar properties.

Answer 2

atoms react depending on the number of electrons in their outermost orbit. so elements in the same group have same number of valence electrons i.e. electrons in t he outermost orbit and therefore they have similar chemical properties