Arrange the following in increasing order of basicity.

The electronic configuration of N is 1s² 2s² 2p³ . 's' and 'p' orbital of nitrogen atom requires energy in order to for the hybrid orbital . and after that it will combine with three hydrogen atoms in which energy is released which is greater than  the energy requires for the formation of hybrid orbital . If this condition is satisfies than only bond is formed . but in case of  phosphorus and higher elements these compensation of energy is not that much which compensate the energy of hybridization . hence each P orbital overlap individually & hence there bond angle  is around 90 degree and whatever fluctuation about 90 degree is because of replusion . As we move down the  group electron will be then donated form pure 's' orbital . Hence,  the correct order is BiH₃ <  SbH₃ < AsH₃ < PH₃ < NH₃ .