Why can't you say "this is much"? if for instance you talk about milk? Is "This is a lot" the only acceptable answer? I tried some others, nothing worked.
Thank you for the explanation but some of these "rules" you mentioned I don't think exist or at least I'd never heard before, and although I'm not a native speaker, I'm by no means a beginner either. Can you please show where you found these rules?
Never heard a native speaker (myself included) use this sentence. Also years of studying and teaching from "The Grammar Book: An ESL/EFL Teacher's Guide" by Diane Larsen-Freeman and Marianne Celce-Murcia. Also Cambridge Online Dictionary. For a quick check, type "It is much." into Google - it appears nowhere as a complete sentence.
Another arrogant response.... You made a statement, it's you who needs to back it up.
Apologies that you perceived arrogance in the response. Much can be confusing in English. In order to be used as a short answer to a question, it needs to be modified: "It is TOO much"; "It is NOT much"... and in both of these cases the noun is dropped only because it was made obvious in the preceding question (e.g. How much money is it? It is too much money.) Even if you were trying to answer a question about a non-count noun like money, (How much (money) is it?) You couldn't answer using "much" (It is much) but would have to use "a lot" because the answer is an affirmative (It is a lot (of money).) If the reply were negative, we could use, "It is NOT much (money)." You could also use "much" before an adverb of degree (e.g. It is much appreciated/admired/enjoyed). But again, not on its own. I hope the explanation helps you understand why "It is much." is not a complete English sentence.