I would like to know, If I have password of a wifi-router? and I know the MAC address and IP of Target Iphone using this wifi-router, can I get to contents of social media like WhatsApp chats?
Most traffic these days use additional encryption. Things like facebook chat only use TLS between the server and client, whilst WhatsApp uses the Signal protocol for true end to end-encryption. You can not get access to this by intercepting the traffic at the IP layer.