32 bits or 30 bits for subnet mask

I'm new to networking and have a question about subnet masks. Imagine we have a class B IP address. I know how to calculate the subnet mask. My question is: What is the last subnet mask that we can use for this IP. In case of subnetting, can we use 255.255.255.255 for this IP as the subnet mask or the last subnet mask that we can use is 255.255.255.252?

I mean can we use all 32 bits in the creation of the subnet mask or we can only use 30 bits?