What is the collective noun for a stack of paper?
The collective noun is 'stack'.
Yes, it can. A collective noun is an informal part of language. Any noun that suits the context can function as a collective noun. The standard collective noun for 'books' is a library of books, but the noun 'pile' or 'stack' may be more suitable for the situation. Similarly, nouns such as 'a shelf', 'a bag', or 'an armload' may suitable for another situation.
There is not collective noun for the word 'loaf'. A collective noun is a word for a group of things; the noun loaf is a singular, one loaf. The plural noun is 'loaves'. Some collective nouns for loaves are a batch of loaves or a stack of loaves. Other collective nouns for loaves would be a word suitable for the context of the loaves; for example a basket of loaves, a shelf of loaves, a…