Question

what is the size of a register called? (how many bits it can store)
stack
length
width
gate
rewatch

Explanation:

In computer science (a sub - field of Natural Science), the size of a register (the number of bits it can store) is referred to as its width. A stack is a data structure. Length is a more general term not specific to register bit - storage. A gate is a basic building block in digital circuits (like logic gates) and not related to register size in this context.

Answer:

Width