So you're an adept of the literal translation. However I think a native English speaker would rather use the plural to convey the same meaning.
Yes, but this gives you better insight into how Hindi-speakers think. There is a singular mental type of the object in question, which doesn't require the concept of plurality to indicate generality.
yes, but lets not stop here and continue to take the best insight into how Hindi-speakers think... For that... 'rat small generally is' should be accepted as the only correct answer.
Chuha chota hai = The rat is small.
Chuha chota hota hai = A rat is (generally) small.
"hota" makes the sentence like a statement of fact about all rats.
This is really annoying... It uses होता therefore this is a case of generalisation. It should accept '(the) rats are ...'
The worst "reason" I've seen so far is "context". Either give me the context or accept every answer that could be valid in any reasobable context applicable to the phrase.