Question

why does the boiling point increases down the group in 15th group elements??on what factor does the boiling point of a substance depends??

Answer 1

Boiling point increases down the group due to the increase in the vander waals forces of attraction. As we go down the group size of the atom increases, this increase in the size means that the strength of ​vander waals forces of attraction also increases. And as the strength increases we require more energy to break the bonds to change it into gas phase. Thus the boiling point increases.
Factors on which the boiling point depends -
1) Strength of bonds- If the bond is stronger, then boiling point is high.
2) It depends on the size of the atoms
3) Branching decreases the boiling point as it decrease the surface area.