opened a library for the module on Arduins, there is a type of entry
# define addr_mask 0x1f
1F I understand some byte in a hexadecimal calculus system, and what is
0x and why is it necessary?
Answer 1, Authority 100%
This is an ordinary integral literal recorded in a sixteenty-old number system. There are other prefixes, in more detail in the corresponding section:
Integral Literal , Character Literal , Floating Literal etc.