How many of the following are inert to hydrolysis

$B{F_{3,}}_{ }SiC{l}_4,PC{l}_5,S{F}_6$

Boron tri flouride is inert to hydrolysis due to the concept of Back bonding, where B-F gains partial double bond charecter due to the donation of p-orbital electrons of flourine to the vacant orbital of boron, the concept of back bonding.