Answer:
What is the valency of elements in the group 'v' of the modern periodic table?
Answer: -3
What is the reasons for the fact that reactivity of group 'v' elements decrease as we go down in the group?
Answer: On moving down the group, there is a decrease in the electron affinity of elements. It is because, as the size of an atom increases, the valence electrons get further away from its nucleus. Thus, the attraction between them decreases.