1. what are interhalogen compounds????
2. why pcl3 and pcl5 are not interhalogen compounds????

Kindly refer to the following link:
 
https://www.meritnation.com/ask-answer/question/what-are-interhalogen-compounds/chemistry/6086775

PCl₃ and PCl₅ are not considered as interhalogen compounds because P is not a halogen atom.