Write main differences between the properties of white phosphorus and red phosphorus. 

The difference in the bond angles is based on the electronegativity and the size of the central atom. For example, nitrogen is the smallest in size with maximum elctronegativity (3.0). The electron density is very hgh around nitrogen which also means strong repulsions in the electron pairs around it resulting in maximum bond angle (107°). As we move down the group, the atomic sizes increase and the electronegativities decrease. As a result, there is a gradual decrease in the electron density on the central atom resulting in decreased bond angles in the same order. Thus, the HNH angle value is higher than HPH, HAs H and HSbH angles.

Nitrogen atom has the smallest size and a very high electron density aroun the nitrogen. Therefore, its electron releasing tendency or the basic strength is the maximum. Down the group, there is a gradual increase in atomic size and decrease in the electron density on the central atom. Consequently, the electron releasing tendency or basic strengths of the hydrides decrease in the order as given below

NH₃ > PH₃ > AsH₃ > Sb H₃ > BiH₃

Therefore, NH₃ is basic while BiH₃ is only feebly basic.