Why does the melting point of group 15 elements increases as we move down the group from N to As - Chemistry - The p-Block Elements

Question

Why does the melting point of group 15 elements increases
as we move down the group from N to As and then decreases at Sb and
Bi?

Kumar Sarang · Accepted Answer

The melting point depend on the no of unpaired electrons
present on atom Higher the no of unpaired electron, higher is the
melting point Now the melting point of group 15 elements increases
as we move down the group from N to As these elements have tendency
to involve all the 5 electron both s and p orbital in bonding but
as we move down the group from Sb to Bi, the s orbital electron do
not involve in bonding due to inert pair effect which doesn't allow
extra two electron to involve in increasing the melting point of an
atom

Why does the melting point of group 15 elements increases as we move down the group from N to As and then decreases at Sb and Bi?