does the 855 chip has x50 modem for 5g connectivity ?
No, only a few phones with snapdragon 855 supports 5G. To add 5G is to expensive and very few people will be able to use 5G before we release the next Zenfone and maybe even the Zenfone after that.
It will take much longer before 5G exists in every city than most people think. There are a lot of articles and youtube videos explaining why.
